Mu'min is also a Divine Name, for God is the ultimate Mu'min, the source of security and reliability. We put our trust in, confide in, and rely upon Him. He distinguished the Prophets by their trustworthiness, and our connection to Him through the Prophets is based entirely on their trustworthiness and reliability.
Trustworthiness is also an essential quality of Archangel Gabriel. The Qur'an describes Gabriel as one obeyed and trustworthy (81:21). We received the Qur'an through two trustworthy Messengers: Gabriel and Prophet Muhammad. The former conveyed it; the latter related it to us.
The trustworthiness of God's Messenger. Prophet Muhammad was completely trustworthy toward all of God's creatures. He was loyal and never cheated anyone.
God chose the Messenger for his trustworthiness so that he would devote himself totally to delivering the Message truthfully. He was so concerned about his duty that he would repeat the verses while Gabriel was reciting them to him. God finally revealed: Move not your tongue concerning (the Qur'an) to make haste therewith. It is for Us to collect it, to establish it in your heart and enable you to recite it. So, when We have recited it to you, follow its recital. Then it is also for Us to make it clear to you (75:16–19).
As the Qur'an was given to him as a trust, he conveyed it to people in the best way possible. He dedicated his life to this sacred cause, constantly aware of his responsibility. In the last year of his life, when he was delivering the Farewell Pilgrimage's sermon at Mount 'Arafat, he reiterated the Commandments of God once more. At the end of each sentence, he told the people: "In the near future, they will ask you about me." He then would ask them if he had conveyed the Message to them, to which they responded, each time, with great enthusiasm: "Yes, you have conveyed it!" He then would call upon God to witness their words. 
Specific events demonstrating the Messenger's trustworthiness. God's Messenger never thought of concealing even a word of the Qur'an. In fact, we read in the Qur'an several Divine mild admonitions for a few actions of his. If he wrote it, as some mistakenly claim, why would he have included such verses?
The Prophet was raised in a primitive society characterized by customs that contradicted reason as well as sociological and scientific facts. For example, as adopted children enjoyed the same legal status as natural children, a man could not legally marry his adopted son's widow or ex-wife. This practice was abolished, for adoption does not create a relationship comparable to that with one's biological parents. God solved this problem, as always, through the Messenger's life in order to separate a legal fiction from a natural reality, and to establish a new law and custom.
Zayd, an emancipated black slave and servant of God's Messenger, was also his adopted son. At the Prophet's request, Zayd married Zaynab bint Jahsh. Nevertheless, it soon became clear that the marriage would not last long. Admitting that he was spiritually and intellectually inferior to his wife, Zayd thought it would be better for him to divorce her. In the end, the Qur'an commanded Muhammad to marry her: We gave her in marriage to you (33:37).
Of course, doing so would violate a strong social taboo. As such, and because the Hypocrites would use this to defame him, he delayed announcing the Divine decree. God admonished him as follows: Then you said to him on whom God bestowed grace and unto whom you had shown favor: "Keep your wife to yourself and fear God." But you hid in your heart that which God was about to make manifest because you feared the people [would slander you], whereas God had a better right that you should fear him (33:37). 'A'isha later commented: "If God's Messenger could have concealed any Revelation, he would have concealed that verse." 
If Muhammad had not been trustworthy, he would have done just that. However, such an act is contrary to his character and mission, and would mean that he had not delivered the Message. Furthermore, God prohibits him from doing this: O Messenger, deliver what has been sent down to you from your Lord; for if you do not, you will not have fulfilled your task of His Messengership. God will protect you from men. God does not guide the unbelievers (5:67). So, God's Messenger passed on whatever was revealed to Him.
His relations with others. God's Messenger was trustworthy and encouraged others to follow his example. Once during the last ten days of Ramadan, his wife Safiyya visited him while he was keeping vigil in the mosque. As he was escorting her home, two Companions happened to pass by. The Messenger stopped them and, unveiling his wife's face, said: "This is my wife Safiyya." They said: "God forbid any evil thought about you, O Messenger of God." The Messenger was warning them against having evil thoughts about him, for that could cause them to lose their faith and enter Hell. He gave them and us a lesson, saying: "Satan continuously circulates within people's blood vessels." 
God's Messenger was an embodiment of trustworthiness. His own people, even before his Prophethood, called him al-Amin (the Trustworthy One). After his declaration, his enemies continued to entrust him with their precious goods.
He warned his people against lying, breaking their word, and breaching their trust. All of these were condemned as "signs of hypocrisy."  He was so meticulous in this matter that when he saw a woman call her child, saying: "Come on, I'll give you something," he asked her if she was telling the truth. She replied that she would give him a date, to which God's Messenger responded: "If you don't give him something, you are a liar."
His concern in this matter extended even to animals. Once, annoyed at seeing a Companion trying to deceive his horse, he said: "Stop deceiving animals. Instead, be trustworthy with them."  Another time, while returning from a military campaign, a few Companions took some baby birds from a nest to pet them. The mother bird returned after a short while and, finding her babies gone, began to fly around in distress. When God's Messenger was informed, he was so upset that he ordered the babies returned immediately. Such an order was meant to show that representatives of trustworthiness should harm no living creatures. 
Each Companion was an embodiment of trustworthiness. By virtue of this and other laudable virtues, cities and states submitted to Islam. During 'Umar's caliphate, Abu 'Ubayda, the embodiment of justice, commanded the Muslim armies in Syria. When the Byzantine Emperor set out to recapture Hims, Abu 'Ubayda decided to evacuate the city, for his forces were vastly outnumbered. He had the non-Muslim population assembled and announced: "We collected the protection tax from you because we had to defend you. Since we can't defend you against the coming Byzantine assault, we are returning the tax we collected." This was done. Pleased with the Muslim administration, Christian priests and Jewish rabbis flocked to the churches and synagogues to pray that God would cause the Muslim army to be successful. 
Such was the attitude of Muslim conquerors and administrators in the lands they ruled. Muslims stayed in Spain for eight centuries. If there were enough Christians left to acquire enough power to expel the Muslims later on, it was because of the Muslim administration's religious tolerance. Muslim rulers did not interfere with a conquered people's religion, language, or culture. If they had done so, there would have been no Christians left to recapture Spain, no Jews left to conquer Palestine, and no Christians left in the Balkans to engage in genocide. Nor would Christians have been able to destroy peoples, cultures, and languages on an almost-global scale.
Islam emphasizes trustworthiness and security to such an extent that suspicion and gossip are forbidden:
O you who believe! Avoid much suspicion, for suspicion in some cases is a grave sin. Do not spy on or gossip about one another. Would one of you like to eat the flesh of his dead brother? You would abhor it. Fear God, for verily God is the Acceptor of repentance, the Most Merciful. (49:12)
God's Messenger was so sensitive on this point that once when 'A'isha commented: "How long her neck is," he said: "You have gossiped about her and thereby eaten of her flesh!" 
 Bukhari, Tawhid, 22; Muslim, Iman, 288.
 Bukhari, I'tiqaf, 8; Ibn Maja, Siyam, 65.
 Abu Dawud, Adab, 80; Ibn Hanbal, 3:447.
 Bukhari, Iman, 24; Muslim, Iman, 107.
 Abu Davud, Jihad, 112, Adab, 164; Ibn Hanbal, 1:404.
 Abu Dawud, Adab, 164; Ibn Hanbal, 1:404.
 Ibn Kathir, Tafsir, 7:359; Al-Targhib wa al–Tarhib, 4:285.
God's Messenger always prayed: "O God, I seek refuge in You from hunger, for how bad a companion it is! I also seek refuge in You from betrayal, for what an evil confidant it is!"  He also had harsh words for those who betray and are disloyal: "When God gathers together on the Day of Judgment all the people preceding and to come, a banner will be raised on behalf of every disloyal person. It will be announced: 'This is because of the disloyalty of so and so!'" 
The heart of God's Messenger was closed to all evil, but open to all good. He lived in a climate of security, faithfulness, and trustworthiness. He never cheated, lied, betrayed people, just as he never gossiped about, slandered, or harbored evil suspicion about someone. In return, people relied on him and confided in him. His enemies slandered him, but no one ever accused him of lying and disloyalty. Those who turned their backs on him were deceived and dragged into wrong ways.
God's Messenger was totally reliable. His trustworthiness had two aspects: his relationship with people, and his relationship with God. The former manifested itself as complete reliability; the latter as perfect reliance on God. When combined, these two aspects ensure a peaceful atmosphere of steadfastness and security.
The Qur'an gives several examples concerning the Prophets' confidence in, and perfect reliance on, God. To cite only a few:
And recite to them the news of Noah, when he said to his people: "O my people! If my stay (with you) and my reminding (you) of the signs of God is unbearable to you, then I put my trust in God. So come together with your partners and come to an agreement on your plan! Then let not your affair be a worry to you. Pass your sentence on me, and give me no respite. (10:71)
[Hud) said to his people:] I call God to witness and bear you witness that I am free from all that you ascribe as partners in worship to God, beside Him. So, plot against me, all of you, and give me no respite. I put my trust in God, my Lord and your Lord. There's not a moving creature but He has grasp of its forelock. Verily my Lord is on a straight path. (11:54–56)
Indeed there has been an excellent example for you in Abraham and those with him, when they said to their people: "Verily we are free from you and from whatever you worship besides God; we have rejected you, and there has arisen between us and you hostility and hatred for ever, until you believe in God alone,"—except Abraham's saying to his father: "Verily I ask forgiveness (from God) for you, but I have no power to do anything for you before God. Our Lord! In you (alone) we put our trust, and to You (alone) we return in repentance, and to You (alone) is our final return." (60:4)
The nature of unbelief is deviation and opposition. Unbelievers see the world in darkness and feel alone in an alien world; believers see the whole universe as a cradle of brotherhood and sisterhood, and feel connected to everything. By its nature, unbelief severs relations and, as a result, unbelievers feel enmity against everything, especially believers. They cannot bear the believers' existence, so they try their best to eradicate belief. That is why all Prophets encountered severe opposition and, with their followers, suffered pitiless acts of cruelty. But due to their complete confidence in and perfect reliance on God, they never lost heart because of what befell them in God's Way, nor did they weaken (in will) nor were they brought low (3:146).
The Messenger's reliance on God made him fearless. He appeared in the heartland of a desert inhabited by one of the most uncivilized peoples. Despite their harsh treatment, and the strident hostility of one of his own uncles, he challenged the whole world and, through complete trust in God, carried his mission to victory. He had only a handful of supporters, and his victory came in a very short period—an unparalleled achievement. We can understand his fearless nature, which developed out of his absolute confidence in God, through the following anecdotes.
The Quraysh were so eager to kill him that just before his emigration to Madina they selected one man from each clan. These numbered roughly 200. Led by Abu Jahl and Abu Lahab, then besieged his house. God's Messenger told his cousin 'Ali to spend the night in his bed and, throwing some dust at the hostile men while reciting: We have put a barrier before them and behind them, and thus covered them so that they cannot see (36:9), he departed without being seen.  He left Makka with his closest friend, Abu Bakr, and reached Thawr cave, which is at the top of a steep mountain. Finding him gone, the Qurayshi chiefs sent out search parties. One of these climbed the mountain up to the cave. Abu Bakr became anxious, fearing for the life of God's Messenger. However, the latter comforted him: Do not be anxious, for God is with us (9:40), and added: "What do you think of the two men beside whom God is the third?" 
In the Battle of Hunayn, the Muslim army was forced to retreat. All but a few thought they were about to lose. God's Messenger spurred his horse forward and shouted: "I am a Prophet. This is not a lie! I am the son of 'Abd al-Muttalib!"  His courage and steadfastness were enough for his Companions to collect themselves and ultimately be victorious.
As related through various channels, during the military campaigns of Ghatfan and Anmar, a courageous chieftain named Ghowras unexpectedly appeared beside God's Messenger, who was lying under a tree. Unsheathing his sword, he asked God's Messenger: "Who will save you from me now?' "God," the Messenger replied, and then prayed: "O God, protect me against him as You will." At that moment, Ghowras was knocked down and his sword slipped from his hand. God's Messenger picked it up and asked him: "Now, who will save you from me?" Ghowras began to tremble and pleaded for his life: "You are a noble, forgiving man; only forgiveness is expected of you." God's Messenger forgave him, and when Ghowras returned to his tribe, he said: "I have just come from the best of humanity." 
Trustworthiness is a cornerstone of belief:
God commands you to give the trust to (the charge of) those qualified for them, and when you judge between men, to judge with justice. How excellent is the teaching which He gives you! Truly God is All-Hearing, All-Seeing (4:58).
According to God's Messenger, breaching a trust is a sign of the end of time: "When a trust is breached, expect the end of time." When his Companions asked how a trust would be breached, he answered: "If a job or post is assigned to the unqualified, expect the end of time." 
Assigning qualified people to jobs or posts is a social trust and plays a significant role in public administration and social order. Its abuse causes social disorder. There should be order at all social levels, for some are to be given responsibilities by others. God's Messenger declared: "Each of you is a shepherd [manager], and each of you is responsible for your flock. The ruler is a shepherd responsible for his subjects. A husband is a shepherd responsible for his family. A woman is a shepherd responsible for her husband's house. A servant is a shepherd responsible for managing the duties or property his master entrusted to him."  If everyone in a society were to carry out their responsibilities, we would be living in a "society of trustworthy ones." Until that time, we can only imagine such utopias.
Trustworthiness is so essential an aspect of belief that God's Messenger once declared: "One who is not trustworthy is not a believer,"  and described a believer as one whom the people trust with their blood and property.  Furthermore, he said: "Promise me the following six things and I will promise you Paradise: When you speak, speak the truth; when you give a promise, carry it out; when something is entrusted to you, do not breach it; keep chaste and don't engage in illicit sexual relations; don't look at what is forbidden; and don't grasp what is forbidden."  Even looking with lust at one to whom you are not married is forbidden: "God says: "[Such] a glance is like a poisonous arrow from Satan's quiver. Whoever refrains out of fear of Me, I inculcate belief so firmly in their hearts that they will taste it." 
To live in absolute security is only possible if trustworthy people are in power. If the Muslim world observes the Divine Trust and becomes the representative of trustworthiness and security in the world, a "new world order" based on justice and balance will be possible. Otherwise, humanity will continue to chase after mirages of justice, security, and happiness.
Through his truthfulness, trustworthiness, and other laudable virtues, God's Messenger left an indelible mark on people of all ages. His every word and deed proclaimed his Messengership, that he was sent to guide people to truth, to bring them out of the darkness of ignorance and savagery, slavery and immorality, into the light of knowledge, high morality and love, compassion and true freedom.
 Muslim, Jihad, 9.
 Ibn Hisham, Sira, 2:27.
 Bukhari, Tafsir, 9; Ibn Hanbal, 1:4.
 Bukhari, Jihad, 52; Muslim, Jihad, 78.
 Bukhari, Maghazi, 29, Jihad, 83; Muslim, Fada'il, 13.
 Bukhari, 'Ilm, 2; Ibn Hanbal, 3,361.
 Bukhari, Jumu'a, 10; Muslim, 'Imara, 20; Abu Dawud, 'Imara, 1.
 Ibn Hanbal, 3:135.
 Tirmidhi, Iman, 12; Ibn Ma'ja, Fitan, 2.
 Ibn Hanbal, 5:323.
 Hindi, Kanz al-'Ummal, 5:328.