http://www.answering-islam.org/Christians/index.html Islamic studies by author (non-Muslim or academic) 622 to 1500 Joannis Damasceni (c. 676-749), official of the Caliph at Damascus , later a Syrian monk , Doctor of the Church , his Peri Aireseon [Concerning Heresies] [t], its chapter 100 being " Heresy of the Ishmailites " (attribution questioned). Du