Hussain Kamani – 40 Ahadith of Imam An-Nawawi 14 – The Honor Of Human Life

Ibn Masood (r) who said:
The Messenger of Allah (s) said, It is not permissible to spill the blood of a Muslim except in three [instances]: the married person who commits adultery, a life for a life, and the one who forsakes his religion and separates from the community. (Bukhari & Muslim)