The Messenger, always aware of developments bearing on his mission, promptly decided to challenge the Byzantines on the battlefield. Any show of Muslim weakness might have revived the dying forces of Arabian polytheism and hostility, which had received a crushing blow at Hunayn. Such a development also could encourage the Hypocrites in and around Madina to cause serious damage to Islam from within. They already were in touch with the Ghassanid Christian prince and with the Byzantine Emperor, and had built a mosque—which the Qur'an calls the Mosque of Dirar (Dissension) (9:107)—near Madina to serve as their operational base.
Realizing the gravity of the situation, the Messenger publicly appealed to the Muslims to prepare for war and, against his usual practice, declared that the Byzantines were his target.
It was mid-summer. The scorching heat was at its peak, the harvest season had just arrived, and there was a shortage of material resources. What was more, the enemy was one of the two current superpowers. Despite all this, the Companions responded ardently to his call and commenced their war preparations, all contributing much more than their financial means warranted. Huge amounts of money were donated by such wealthy Companions as 'Uthman and 'Abd al-Rahman ibn al-'Awf.  Those who could not be included in the Muslim army, due to shortages of riding animals and other necessary supplies, wept so bitterly and lamented their exclusion so pathetically that the Messenger was moved. God praised them in Qur'an 9:92. The occasion, in fact, served as a touchstone for distinguishing the sincere from the insincere, the believers from the Hypocrites.
In Rajab 9 ah/631 ce the Messenger and 30,000 soldiers left Madina and marched to Tabuk, quite close to what was then Byzantine territory in Syria. The Byzantine Emperor, who had begun amassing a huge army, abandoned his plans and withdrew his army, for the Messenger arrived before he was expected and well before Byzantine troop concentrations were completed. 
The Messenger stayed in Tabuk for 20 days, and forced several buffer states under Byzantine hegemony to pay the poll tax (jizya) and live under his rule. Many Christian tribes embraced Islam willingly.  This bloodless victory enabled the Muslims to consolidate their position before launching a prolonged conflict with the Byzantines, and shattered the power of both unbelievers and Hypocrites in Arabia.
 Ibn Sa'd, 2:165–8; Tabari, Tarikh, 3:100–11.
 Ibn Kathir, al-Bidaya, 5:13.