Sunan Ibn Majah Book 20, Hadith 1
`Uthman bin 'Affan looked at them when they spoke of killing. He said: “Are they kill threatening to kill me? Why would they kill me? I heard the Messenger of Allah (ﷺ) say: “It is not lawful to shed the blood of a Muslim except in one of three (cases): a man who commits adultery when he is a married person, then he should be stoned; a man who kills a soul not in retaliation for murder; and a man who apostatizes after becoming Muslim.' By Allah (SWT), I never committed adultery either during Ignorance days nor in Islam, and I have never killed a Muslim soul, and I have not apostatized since I became Muslim.”
`Aishah had a male slave and a female slave who were married. She said: “O Messenger of Allah (ﷺ), I want to free them both.” The Messenger of Allah (ﷺ) said: “If you free them, then start with the man before the woman.”
“It is not lawful to shed the blood of a Muslim who bears witness that none has the right to be worshiped but Allah (SWT), and that I am the Messenger of Allah (ﷺ), except in one of three cases: a soul for a soul; a married person who commits adultery, and one who leaves his religion and splits from the Jama`ah.”