Nice question,
They (sunni,shia,alevi,wahhabi etc) have interesting claims for this, the sects are shaped according to "hadiths", Quran verses prohobits to believe in anything other than Quran as a source for Islam. So Allah says the only source for Islam is Quran, nothing else. But there are also some verses that orders to follow or obey prophet. Hadith followers always suggest these verses for their beliefs in "hadiths", but if you look at these verses carefully, you can easily realize that these verses orders to follow or obey prophet for people who were living in the time of the Prophet. Collecting stories about the prophet is not to following prophet, Quran also says obey to the people who have the authority on you, your father, your chief, your president, your teacher etc, why do muslims not collecting "hadiths" about these people ? Why they change their attitudes ? They contradict with themselves.