During the time of Abu Bakr the Muslims captured a greater part of Syria including Damascus. When Umar became the Caliph the Byzantines made strong preparations and concentrated a very large army at Yermuk with a view to expelling the Muslims from Syria. The Muslims had to evacuate Damascus, and the cities in Northern Syria with a view to facing the Byzantines in battle at Yermuk in Southern Syria. It was a critical state of affairs for the Muslims. At this juncture Umar was of the view that he should himself go to Syria to command the Muslim forces. Umar sought the advice of Ali on the point. Ali advised in the following terms: "God is the protector of the Muslims. He guards their secrets. God helped the Muslims when they were few in number, and could not face the enemy. God defended them when they could not defend themselves. When God helped the Muslims in the early years, we can depend on His help even now when we have gained in numbers. God is alive, and would never die. We are fighting in His cause. And we should have perfect faith that He would help us. If you yourself go to fight against the Byzantine and God forbid are defeated, that will cause a great confusion, and would demoralize the Muslims. That would create a precarious situation for the Muslims in the areas bordering Syria. The proper course for you would be to remain in Madina, and direct the operations from there. You may place a seasoned general in command of the Muslim forces in Syria. God willing, the Muslims would be victorious. "Umar acted on the advice of Ali, and the Muslims won an astounding victory at the Battle of Yermuk.