Here’s an excerpt from a very interesting article by Daniel Pipes (it wouldn’t surprise me one bit if it’s all a fabrication ala Joseph Smith and the Golden Plates):
Noting that coins and inscriptions from the seventh century mention neither Muhammad, the Koran, nor Islam, they conclude that the new religion did not appear until about 70 years after Muhammad’s supposed death. Spencer finds that “the first decades of the Arab conquest show the conquerors holding not to Islam as we know it but to a vague creed [Hagarism, focused on Abraham and Ishmael] with ties to some form of Christianity and Judaism.”
In very brief: “the Muhammad of Islamic tradition did not exist, or if he did, he was substantially different from how that tradition portrays him” – namely an Anti-Trinitarian Christian rebel leader in Arabia.
Only about 700 A.D., when the rulers of a now-vast Arabian empire felt the need for a unifying political theology, did they cobble together the Islamic religion.