Sunan Abu Dawud
4352
Sahih+3

Abd Allah (b. Mas`ud) reported the Messenger of Allah (peace be upon him) as saying:The blood of a Muslim man who testifies that there is no god but Allah and that I am the Messenger of Allah should not be lawfully shed but only for one of three reasons: married fornicator, soul for soul, and one who deserts his religion separating himself from the community

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid