I'm interested in learning more about Muhammad the Prophet during his time as a merchant, in order to write an essay. Would it be possible to find out how much his time as a merchant and a manager of his wife's business influenced the writing of his Islamic law and Surahs? Any help finding academic sources to use for citations would be greatly appreciated.
Reliably writing anything about the life of the prophet is more easily said than done.
The primary basis for his life story comes from the sira/maghazi literature (the prophetic biography and tales of his raids) as well as the hadith, the collected reports of his sayings and descriptions of his actions.
The problem is that these were written down hundreds of years after the fact, and there are very serious reasons to believe that these tales are spurious.
In other words, rather than his life influencing Islamic law, it seems that in large part the development of Islamic law required the fabrication of details about the life of Muhammad.
I would read Robert Hoyland's essay Writing the Biography of the Prophet Muhammad: Problems and Solutions which is a great overview of these problems.
That being said, if this is maybe a high school essay it might not be necessary to engage in serious source criticism. If you're OK with that, then I would look to either the Sira itself (the most accessible version of which is A. Guillaume's The Life of Muhammad which is a translation of the Sira of ibn Ishaq/ibn Hisham. Alternatively W. Montgomery Watt's Muhammad: Prophet and Statesman might be a more accessible text.
Even more accessible would be Michael Cook's Muhammad or Jonathan A.C. Brown's Muhammad: A Very Short Introduction both of which are about 100 pages.
For a revisionist take on what trade in Arabia was like in the lifetime of the prophet see Patricia Crone's Meccan Trade and the Rise of Islam, though I would be cautious about her radical alternative proposals. Reviews of her work on JSTOR make for a nice counterpoint.
For the structure and development of the Qur'an the introductory chapters of Neal Robinson's Discovering the Qur'an are quite good.
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