The bizarre hadith of Bukhari and Abu Dawud.
From Introduction to The Book of Hadith:
It cannot be denied that there has been an unwarranted elevation over time of the Hadith as a source of guidance in competition with the Qur’an itself, to the extent that verses of the Qur’an which appear to conflict with favourite Hadith may be declared to be abrogated by other verses which agree with the Hadith in question. This idolization of Hadith contradicts the incontrovertible truth that the Qur’an alone should always be referred to as infallible guidance even if the Hadith have been second only to the Qur’an as the basis of Islamic law.
One striking example will suffice to show the many conflicts between the Qur’an and the Hadith: The Qur’an clearly allows freedom of religion, but both Bukhari and Abu Dawud include the bizarre Hadith, If anyone leaves his religion, then kill him. (Bukhari 52:260). Similarly, a very early source, the Al-Muwatta’ of Malik ibn Anas (d.179/795), states that anyone who leaves Islam for something else and divulges it is called upon to repent, but if he does not turn in repentance, he is killed. The penalty of death for apostasy is repeated elsewhere in Bukhari: Whoever changes his Islamic religion, then kill him (Bukhari 84:57). Another Hadith (Bukhari 83:37) holds that death is required in three cases: for a murderer, for a married person committing illegal sexual intercourse, and for one who deserts Islam. In this last case, historical evidence makes it clear that the apostates referred to here can be identified with those who are waging war against the Muslim community, and I will return to this critical point in due course.
The most oft-quoted Hadith in Bukhari, If anyone leaves his religion, then kill him, can be questioned on the grounds that its chain of transmission (isnad) goes through a source whose narrations were rejected by Imam Muslim because of the accusations of some scholars that the man concerned (‘Ikrimah) was a liar who also accepted gifts from various political authorities.