Among his own people, Prophet Muhammad was famous for his trustworthiness even before his proclamation of Prophethood. He was known as al-Amin (the Trustworthy). Like his predecessors, he asked no wage for calling to God.
Prophets never thought of material gain, spiritual reward, or even Paradise—they strove only for God's good pleasure and to see humanity guided to the truth. Prophet Muhammad was the foremost in this respect. As he devoted his life to humanity's welfare in this world, he will do so in the Place of Gathering. While everybody else will care only about themselves, he will prostrate before God, pray for the Muslims' salvation, and intercede with God on behalf of others. 
Those who intend to spread the perennial values of Islam should follow these practices. Any message based on an impure intention, regardless of eloquence, will have no effect on people. This point is frequently emphasized in the Qur'an: Follow such as ask no wage of you, that are right-guided (36:21).
Imam Busiri expresses the altruism, sincerity, and patience of God's Messenger in vivid language: "Mountains desired to run on his either side in heaps of gold, but he refused." The Messenger once said: "A day comes when I am hungry so as to endure it with patience; on another day I am full to praise my Lord, acquiring thus the reward of both patience and praising."
'A'isha reported that sometimes was no food was cooked for four successive days in their house.  Abu Hurayra also reports: "Once I went into the Prophet's room. He was praying while seated and groaning. I asked him if he was ill. He replied that he was too hungry to stand. I began to sob bitterly, but he stopped me, saying: "Don't cry, for one who endures hunger here will be safe from God's torment in the next." 
One day, he told Gabriel: "It has been several days since someone has lit a fire to cook food in the house of Muhammad's family An angel appeared and asked: "O Messenger of God, God greets you and asks if you would like to be a Prophet-king or a Prophet-slave?" He turned to Gabriel, who recommended humility. The Prophet raised his voice and replied: "I wish to be a Prophet-slave, who entreats God in hunger one day and thanks Him in satisfaction the next." 
God's Messenger used to eat with slaves and servants. Once a woman saw him eating and remarked: "He's eating as if he were a slave." God's Messenger responded: "Could there be a better slave than me? I am a slave of God." 
God's Messenger is, by virtue of being a slave of God, our master and that of creation, as eloquently stated by Ghalib Dada:
An exalted king, the King of the Messengers, O my Master.
You are an endless source of help for the helpless, O my Master.
God honored you by swearing by your life in the Qur'an, O my Master.
In the Divine Presence, you are the greatest, O my Master.
You are the beloved, lauded and praised one of God, O my Master.
Our "eternal" king you are, sent to us by God, O my Master.
 Bukhari, Riqaq, 17; Muslim, Zuhd, 28.
 Muttaqi al-Hindi, Kanz al-'Ummal, 7:199.
 Ibn Hanbal, 2:231; Al-Hindi, 7:191; Haythami, Majma' al-Zawa'id, 9:18–19.
 Haythami, 9:21.