What is your source for this statement, other than the Koran,
which, in my view, is as reliable as the Iliad?
"Although [the Arabs] were convinced of their close relationship, they were unable to get a consensus from their multitude, for they were divided from each other by religion. In that period a certain one of them, a man of the sons of Ishmael named Muhammad, became prominent [t'ankangar]. A sermon about the Way of Truth, supposedly at God's command, was revealed to them, and [Muhammad] taught them to recognize the God of Abraham, especially since he was informed and knowledgeable about Mosaic history. Because the command had come from on High, he ordered them all to assemble together and to unite in faith. Abandonning the reverence of vain things, they turned toward the living God, who had appeared to their father--Abraham. Muhammad legislated that they were not to [123] eat carrion, not to drink wine, not to speak falsehoods, and not to commit adultery. He said: "God promised that country to Abraham and to his son after him, for eternity. And what had been promised was fulfilled during that time when [God] loved Israel. Now, however, you are the sons of Abraham, and God shall fulfill the promise made to Abraham and his son on you. Only love the God of Abraham, and go and take the country which God gave to your father Abraham. No one can successfully resist you in war, since God is with you".
It goes on to describe early battles in Syria and Palestine, and the victory of the Muslims over the Sassanid Persians.