Sayyidina Abdullah ibn Mas’ud (RA) reported that Allah’s Messenger (SAW) said, “The blood of a Muslim person who bears witness that there is no God but Allah and that I am Allah’s Messenger, is not lawful (to shed) except for one of three reasons, (i) a married man commits fornication,
(ii) life for a life, and
(iii) who abandons his religion and separates from his community.”
[Ahmed 3621, Bukhari 6878, Muslim 1676]