Nothing from the contents of Ibn Ishaq is confirmed by inscriptions or other archeological material. Testimonies from non-Muslim contemporaries do no… - Hans Jansen

“for every event which took place in the life of Muhammad, Ibn Ishaq meticulously recorded in his Sira in which month it took place,” and “this meticulous and systematic dating by month which is Ibn Ishaq’s wont, is, of course, one of the main reasons why Western historians classified his book as historiography in the normal sense of that word.”... “How then,” asks Jansen, “is it possible that not a single one of the numerous events Ibn Ishaq describes and attaches a date to, took place during a leap month? If his narrative of the life of Muhammad would be based on historical memories and on real events, however distorted, but remembered by real people, how can half a solar year (or more) remain unmentioned and have disappeared from the record?”... Ibn Ishaq/Ibn Hisham’s biography, Jansen observes, “can only date from a period in which people had forgotten that leap months had once existed.”... “These stories by Ibn Ishaq,” concludes Jansen, “do not attempt to describe memories of events that took place in the past, but they want to convince the reader that the protagonist of these stories, Muhammad, is the Messenger of God.”59

Ibn Warraq's book will either be ignored with deadly thoroughness or cause an enormous riot.