مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3597
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: “The blood of a Muslim man who bears witness that there is no god but Allah and that I am the Messenger of Allah is not permissible except in one of three cases: a married adulterer, a soul for a soul, and one who leaves his religion and separates from the jama'ah (the main body of Muslims)."
Musnad Ahmad 3621lts isnad is saheeh, al-Bukhari (6778) and Muslim (1676)]