(14) باب الْحُكْمِ فِي الْمُرْتَدِّ
It was narrated that 'Uthman bin 'Affan said:
"I heard the Messenger of Allah [SAW] say: 'It is not permissible to shed the blood of a Muslim except in three cases: A man who commits adultery after having married; or one who kills another person, who is to be killed; or who reverts to Kufr after having accepted Islam, who is to be killed.'"
Reference: Sunan an-Nasa'i 4058
In-book reference: Book 37, Hadith 93
English translation: Vol. 5, Book 37, Hadith 4063