There are numerous early references to Islam in non-Islamic sources, many have been collected in historiographer Robert G. Hoyland's compilation Seeing Islam As Others Saw It. One of the first books to analyze these works was Hagarism authored by Michael Cook and Patricia Crone. Hagarism concludes that looking at the early non-Islamic sources provides a much different and more accurate picture of early Islamic history than the later Islamic sources do, although its thesis has little acceptance. For some, the date of composition is controversial. Some provide an account of early Islam which significantly contradicts the traditional Islamic accounts of two centuries later.
In her book Meccan Trade And The Rise Of Islam, Crone states:
If one storyteller should happen to mention a raid, the next one would tell you the exact date of this raid, and the third one would furnish you even more details. Waqidi (d. 823), who wrote years after Ibn Ishaq (d. 768), will always give precise dates, locations, names, where Ibn Ishaq has none, accounts of what triggered the expedition, miscellaneous information to lend color to the event, as well as reasons why, as was usually the case, no fighting took place. No wonder that scholars are fond of Waqidi: where else does one find such wonderfully precise information about everything one wishes to know? But given that this information was all unknown to Ibn Ishaq, its value is doubtful in the extreme. And if spurious information accumulated at this rate in the two generations between Ibn Ishaq and Waqidi, it is hard to avoid the conclusion that even more must have accumulated in the three generations between the Prophet and Ibn Ishaq
