Musannaf Ibn Abi Shayba 18:1177

Abu Bakr narrated to us, he said: Waki' narrated to us, he said: Al-A'mash narrated to us, from Abdullah ibn Murrah, from Masruq, from Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The blood of a person who testifies that there is no god but Allah and that I am the Messenger of Allah is not lawful except for one of three individuals: a life for a life, the married adulterer, and the one who abandons his religion, separating from the community."