It was a Syrian Christian Monk who first recognized Muhammed as a Prophet. He is reputed to have had children with an Egyptian Christian woman while in exile there. He had very close ties with the Jewish communities of Mecca and Medina.
Muhammed was a syncretist, combining Jewish elements with Christian, to create a new religion. Of course, he was also a bloodthirsty brigand, thorough-going terrorist, child molester, and probably a complete nut-job.
All of these threads exist in Islam today.