Maimonides' The Epistle to the Jews of Yemen was written in about 1172 in reply to inquiries by Jacob ben Netan'el al-Fayyūmi, who headed the Jewish community in Yemen. At that time, the Jews of Yemen were experiencing a crisis—hardly unfamiliar to Maimonides—as they were being forced to convert to Islam, a campaign launched in about 1165 by 'Abd-al-Nabī ibn Mahdi. Maimonides provided the Yemenite Jewish communal leader with guidance, and what encouragement he could muster. The Epistle to the Jews of Yemen provides an unflinchingly honest view of what Maimonides thought of the Muslim prophet Muhammad, or "the Madman" as he calls him, and about Islam generally. Maimonides writes:
http://www.andrewbostom.org/blog/2007/12/26/maimonides-and-the-%E2%80%9Cmeshugga%E2%80%9D-prophet/