John of Damascus wrote barely a dozen pages on Islam despite his position.

Evidence

John occupied a key—and at times awkward—position at the intersection of the Christian and Muslim worlds. Yet in his works, which run to more than fifteen hundred pages in the modern edition, barely a dozen pages deal directly with Islam: a short chapter of his Fount of Knowledge and the brief Disputation Between a Saracen and a Christian. If page count is a reliable gauge, iconoclasm is a much larger preoccupation for John than is Islam. Yet his dozen pages on Islam provide a key glimpse at the formation of an apologetic Christian response to Islam, and they were to be read and reread by scores of later Christian writers as they attempted to come to terms with Islam. — John V. Tolan, Saracens, 342