Chapter 45: The Book of Oaths (qasamah), Retaliation and Blood Money
It was narrated from 'Aishah, the Mother of the Believers, that the Messenger of Allah said: "It is not permissible to kill a Muslim except in one of three cases: A adulterer who has been married, who is to be stoned; a man who kills a Muslim deliberately; and a man who leaves Islam and wages war against Allah, the Mighty and Sublime, and His Messenger, who is to be killed, crucified or banished from the land."
Sunan an-Nasa'i 4743