What did Muhammad borrow from Judaism?
In the case of any single instance of borrowing, the proof that the passage is really of Jewish origin must rest on two grounds. First, it must be shown to exist in Judaism, and to prove this we have every facility. Secondly, in order to attain to certainty we must prove that it in really borrowed, i.e., that it is not founded on anything in old Arabian tradition, which Muhammad used largely as a foundation though he disputed some points. Then again we must show that it had its origin in Judaism and not in Christianity. For the complete discussion of the last two points it would be necessary to write two treatises similar to the one on which I am now engaged, of which the respective subjects would be - (1) the points of contact between Islam and the ancient tradition of the Arabs, and (2) the points of contact between Islam and Christianity; and only in this way could certainty on these points be attained. But these investigations would, on the one hand, lead us too far away from our particular subject,
and, on the other, they would require a much more exact treatment than could be given while handling our main subject. Then, too, they are made unnecessary by the means which we use in each individual case, and which will be shown in the different divisions of the work; so that on most points we can without them attain to a high degree of probability, practically sufficient for all scientific purposes. For the sake of clearness, it may be well to divide the material borrowed from Judaism into thoughts belonging to it, and narratives taken from it, and later we shall have to subdivide again.
Thoughts belonging to Judaism which have passed over into the Quran?
The new thoughts borrowed by one religion from another are of a twofold nature. Either they are radically new, there being hitherto in the borrowing religion not even a foreshadowing of them, so that the very conceptions are new, and require accordingly new words for their expression; or else the component parts of these thoughts have long boon in existence but not in this combination, the form in which these conceptions are blended being a novel one, and the view, therefore, which arises from this unusual presentation being new. We must therefore divide this chapter according to these distinctions.