Satanic Verses

Muhammad admitted that a few of the verses which he thought he had received from Gabriel were in fact from Satan. They would be in the surah The Star (al najm) had they not later been renounced.

Great story and it brings to mind some difficult questions regarding the validity of the rest of the Quran. Here is a section from one site and a few links for people who find this topic interesting. This quote is from a Muslim scholar. I try to quote Muslims more than non-Muslims on Islam:

One of the greatest Islamic scholars who wrote a Tafsir was Zamakhshari. He commented on this event as well.Here is his writings, quoted from "The Quran and its Exegesis, by Helmut Gatje, pages 53 - 55, published by Oneworld, Oxford, England [10].

"The faithful rendering of the revelation Zamakhshari on Sura 22:52/51

We have never sent any messenger of prophet before thee, but that Satan cast into his fancy, when he was fancying; but God annuls what Satan casts, then God confirms His signs - surely God is All-knowing, All-wise.

.. The occasion of the sending down of the present verse is the following: As the members of the tribe of the messenger of God turned away from him and took their stand against him and his relatives also opposed him and refused to be guided by what he brought to them, then, as a result of the extreme exasperation concerning their estrangement and as a result of the eager desire and longing that they be converted to Islam, the messenger of God sheltered the wish that nothing would come down to him that could make them shy away. Perhaps he should have been able to use that for the purpose of converting them and causing them to be dissuaded from their error and obstinacy. Now this wish continued in him until the sura called "The Star" (that is, Sura 53) came down. At that time he found himself with this wish in his heart regarding the members of his tribe. Then he began to recite, and when he came to God's words "and Manat, the third, the other" (Sura 53:20), Satan substituted something in accordance with the wish which the messenger of God had sheltered, that is, he whispered something to him which would enable the messenger to announce his wish. In an inadvertent and misleading manner, his tongue hurried on ahead of him, so that he said: "These (goddesses are the) exalted cranes. Their intercession (with God) is to be hoped for."...Yet, the messenger of God was not clear at this point until the protection of God "isma" reached him and he then became attentive again.

Some say that Gabriel drew his attention to it, or that Satan himself spoke those words and brought them to the people's hearing. As soon as the messenger of God prostrated (for prayer) as the end of the sura, all who were present did it with him and felt pleased (that is, the unbelievers felt pleased that their goddesses had been accepted as intercessors with God).

From Here:
Satanic_Verses