The Sources of Islam is Tisdall's earlier book (from 1900) on the same topic. It contains already most of the important material, but being only a third in size (about 100 pages) it is not as thoroughly documented as the later edition (it also has a few minor mistakes that have been corrected in the later edition), but this is the version that has been reprinted many times, probably because it is much quicker to read.A Word to the Wise: Being a defence of the "Sources of Islam" in response to two Muslim reactions to his above book.
Further individual articles
Is the Qur'an a Miracle? contains several chapters discussing legendary sources of the Qur'an.
Biblical Stories in the Qur'an
Related Topics:
Other Qur'an issues
Answering Islam Home Page