Sahih Bukhari
Blood Money (Ad-Diyat)
Volume: 009 / Book Number: 083 / Hadith Number: 17
Narrated 'Abdullah:
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."