Realizing the gravity of the situation, God's Messenger, upon him be peace and blessings, publicly appealed to the Muslims to prepare for war and, as against his usual practice, declared that the Romans were his target.
It was in mid-summer. The scorching heat of the season was at its peak, the harvest season had just arrived, and there was a shortage of material resources needed to wage a war. What was more, the enemy was one of the two super powers of the time. Despite all, the Companions responded ardently to the Prophet's call and commenced their war preparations, each Muslim contributing much more than his financial means warranted. Huge amounts of money were donated by the wealthy Companions such as 'Uthman and 'Abd al-Rahman ibn al-'Awf, (1) and those who could not be included in the Muslim army because of the acute paucity of cavalry and other war provisions wept bitterly, and lamented their exclusion so pathetically that God's Messenger was moved and God praised them in the verse He revealed (al-Tawbah, 9.92). The occasion, in fact, served as a touchstone for distinguishing the sincere from the insincere, the true men of faith from the hypocrites.
In the month of Rajab 9 A.H./631 C.E. God's Messenger, along with 30,000 soldiers, left Madina and marched as far as Tabuk, quite close to what was then Byzantine territory in the province of Syria. The Roman Emperor, who had indeed begun amassing a huge army, had to abandon the idea of an encounter with God's Messenger and withdrew his army because the Messenger arrived ahead of the anticipated time and well before the planned concentration of troops had been completed. (2)
The Messenger stayed in Tabuk for 20 days and forced several buffer states under the hegemony of the Byzantine Empire to pay the poll tax and live under his rule, and many Christian tribes chose Islam willingly. (3) This bloodless victory also enabled the Muslims to consolidate their position before launching a prolonged conflict with the Romans and altogether shattered the power of both unbelievers and the hypocrites in Arabia.
2. I. Sa'd, 2.165–8; Tabari, Tarikh, 3.100–11.
3. I. Kathir, al-Bidayah, 5.13.