Much of early Islamic history comes in the forms of reports about events that were handed down orally and eventually went through a redaction and codification process. The Sira (The Life of Muhammad) is a biographical work based on those reports that was brought together by Ibn Ishaq and then edited and written down by his student, Ibn Hisham (d. 833), and another version which is preserved in the work of al-Tabari (d. 923) - all of whom were Muslims (so it's not Christian propaganda).

Anyway, that book (which is translated into English By A. Guillaume and you can buy on Amazon pretty cheap) gives information on the life of Muhammad, and includes the story about his first revelation, which states - "And I awoke from my sleep, and it was as though these words were written on my heart. Now none of God's creatures was more hateful to me than an (ecstatic) poet or a man possessed - Never shall Quraysh say this of me! I will go to the top of the mountain and throw myself down that I may kill myself and gain rest." (p. 106)