Musnad Abu Ya'la al-Mawsili 152:134

And from Abdullah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The blood of a Muslim man 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: the previously married adulterer, a life for a life, and the one who abandons his religion, separating from the community."