How alarmed they were can be judged from one incident...

How alarmed they were can be judged from one incident: A neighbor of 'Umar knocked at his door in the night. When 'Umar came out and inquired what the matter was, the visitor said a calamity had befallen. 'Umar asked whether the Ghassanids had come. The visitor was perturbed over another matter but the attack of the Ghassanids was considered so imminent that Umar's frst thought went to it.

In order to meet this danger, the Prophet hastily collected a force of 30,000 volunteers with 10,000 horses among them. In spite of the severe famine that had overtaken Najd and Hijaz and the intense heat of the weather, his people rallied around him. Those who were in a position to do so generously donated large sums of money to meet the expenses of the expedition and to buy weapons and armor to those who could not afford to buy them.

This was the first occasion when an appeal for public donations was made, and many Muslims responded generously. An old and very poor woman brought a small quantity of dates as her contribution. Some hypocrites ridiculed her, but the Holy Prophet said that her contribution was more precious in the sight of Allah than that of many people who had contributed only to show off. The Holy Prophet left 'Ali as his deputy in Medina.

'Ali exclaimed with dismay, "Are you leaving me behind?" The Prophet said, "'Ali! Are you not satisfied that you have the same position in relation to me as Aaron had with Moses, except that there is no prophet after me?" The Prophet thereby meant that as Moses had left Aaron behind to look after his people when he went to receive the Commandments, he was likewise leaving 'Ali behind as his deputy to look after the affairs of the Muslims during his absence.

The Prophet marched at the head of this force to Tabuk, a place situated midway between Medina and Damascus. There, they came to know, to their relief, that the news of the Ghassanids' attack was incorrect. Having stayed for twenty-four days at Tabuk, the Muslim army returned to Medina. The Prophet had marched to Tabuk in order to forestall the Ghassanids and the Byzantines, but a certain Western historian has surmised that the aim of this expedition was expansion, viz.

to capture the trade routes leading to the more prosperous towns of Syria.