Ameer al-Mu'mineen Sayyiduna Uthman bin Affan (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "It is not permissible to shed the blood of a Muslim except for one of three reasons: one, for disbelief after faith (that is, after becoming a Muslim, he becomes a disbeliever again); or if he commits adultery after marriage (he will be stoned); or a person who unjustly kills someone, he will be killed in retribution."

Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The blood of any man who testifies that there is no god but Allah and that I am the Messenger of Allah is not lawful, except in three cases (even if he is a Muslim): a life for a life, a married adulterer, and one who leaves his religion and separates from the community of Muslims."