The principal source from which all biographers started and to which they always returned, was the Qorân, the collection of words of Allah spoken by Mohammed in those twenty-two years. Hardly anyone, amongst the "faithful" and the "unfaithful," doubts the generally authentic character of its contents except the Parisian professor Casanova.[1] He tried to prove a little while ago that Mohammed's revelations originally contained the announcement that the HOUR, the final catastrophe, the Last judgment would come during his life. When his death had therefore falsified this prophecy, according to Casanova, the leaders of the young community found themselves obliged to submit the revelations preserved in writing or memory to a thorough revision, to add some which announced the mortality even of the last prophet, and, finally to console the disappointed faithful with the hope of Mohammed's return before the end of the world. This doctrine of the return, mentioned neither in the Qorân nor in the eschatological tradition of later times, according to Casanova was afterwards changed again into the expectation of the Mahdî, the last of Mohammed's deputies, "a Guided of God," who shall be descended from Mohammed, bear his name, resemble him in appearance, and who shall fill the world once more before its end with justice, as it is now filled with injustice and tyranny. [Footnote 1: Paul Casanova, _Mohammed et la fin du monde,_ Paris, 1911. His hypotheses are founded upon Weil's doubts of the authenticity of a few verses of the _Qorân_ (iii., 138; xxxix., 31, etc.), which doubts were sufficiently refuted half a century ago by Nôldeke in his _Geschichte des Qorâns_, 1st edition, p. 197, etc.]