(5) باب ذِكْرِ مَا يَحِلُّ بِهِ دَمُ الْمُسْلِمِ
It was narrated that 'Abdullah said:
"The Messenger of Allah [SAW] said: 'By the One besides Whom there is no other god, it is not permissible to shed the blood of a Muslim who bears witness to La ilaha illalla (there is none worthy of worship except Allah) and that I am the Messenger of Allah, except in three cases: One who leaves Islam and splits away from the Jama'ah, a person who has been married and then commits adultery, and a life for a life.'"
Reference: Sunan an-Nasa'i 4016
In-book reference: Book 37, Hadith 51
English translation: Vol. 5, Book 37, Hadith 4021