His readiness to undergo persecution for his beliefs, the high moral character of the men who believed in him and looked up to him as a leader, and the greatness of his ultimate achievement - all argue his fundamental integrity. To suppose Muhammad an impostor raises more problems that it solves. Moreover, none of the great figures of history is so poorly appreciated in the West as Muhammad... Thus, not merely must we credit Muhammad with essential honesty and integrity of purpose, if we are to understand him at all; if we are to correct the errors we have inherited from the past, we must not forget the conclusive proof is a much stricter requirement than a show of plausibility, and in a matter such as this only to be attained with difficulty.
- W. Montgomery Watt