(5, 6) باب الْقَوَدِ
It was narrated from 'Abdullah that the Messenger of Allah said:
"It is not permissible to shed the blood of a Muslim except in one of three cases: A soul for a soul, a adulterer who has been married, and one who separates leaving his religion."
Reference: Sunan an-Nasa'i 4721
In-book reference: Book 45, Hadith 16
English translation: Vol. 5, Book 45, Hadith 4725