Muslims’ own reason for Ramadan went unknown to nearly all Christian writers.

Evidence

Only the Cluniacs, Peter the Venerable, and the Annotator from whom he presumably gained his knowledge, mention that the fast marks the Night of Power, laylat al-qadar, on which the Qur’an descended upon Muhammad; and even they did not know that the Night occurs (once) during the fast, but spoke of the descent of the Qur’an, as occurring throughout the thirty nights of the month. — Norman Daniel, Islam and the West, 1234