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."