Dr. Bill Warner destroys the idea that Islam can be understood solely through the Koran:
Some of the “reformers” are claiming the Hadith and Sira can be ignored. (This is in fact nothing new, there has been a movement called the Quranist movement for a long time). They want to ignore them because the brutality is a lot more transparent and explicit, for example here is explicit justification for the killing of apostates in the Hadith:
Allah’s Apostle said, “The blood of a Muslim who confesses that none has the right to be worshipped but Allah and that I am His Apostle, cannot be shed except in three cases: In Qisas for murder, a married person who commits illegal sexual intercourse and the one who reverts from Islam (apostate) and leaves the Muslims.”
Dr Bill blows up this idea, that you can ignore the Hadith and the Sira, as follows – the Koran says Mohammed’s life is a beautiful pattern of conduct for Muslims to follow (Koran 33:21), but there is no way of really discovering Mohammed’s life unless you read the Hadith and the Sira. There is very little information about Mohammed’s life in the Koran, he is mentioned by name only 4 (or 5) times in the Koran.