When a slave runs away and reverts to polytheism, he may lawfully be killed.

A blind man had a slave-mother who used to abuse the Prophet (ﷺ) and disparage him. He forbade her but she did not stop. He rebuked her but she did not give up her habit. One night she began to slander the Prophet (ﷺ) and abuse him. So he took a dagger, placed it on her belly, pressed it, and killed her. A child who came between her legs was smeared with the blood that was there. When the morning came, the Prophet (ﷺ) was informed about it.

He assembled the people and said: I adjure by Allah the man who has done this action and I adjure him by my right to him that he should stand up. Jumping over the necks of the people and trembling the man stood up.

He sat before the Prophet (ﷺ) and said: Messenger of Allah! I am her master; she used to abuse you and disparage you. I forbade her, but she did not stop, and I rebuked her, but she did not abandon her habit. I have two sons like pearls from her, and she was my companion. Last night she began to abuse and disparage you. So I took a dagger, put it on her belly and pressed it till I killed her.

Thereupon the Prophet (ﷺ) said: Oh be witness, no retaliation is payable for her blood.

A Jewess used to abuse the Prophet (ﷺ) and disparage him. A man strangled her till she died. The Messenger of Allah (ﷺ) declared that no recompense was payable for her blood.

AbuBarzah said: I was with AbuBakr. He became angry at a man and uttered hot words. I said: Do you permit me, Caliph of the Messenger of Allah (ﷺ), that I cut off his neck? These words of mine removed his anger; he stood and went in. He then sent for me and said: What did you say just now? I said: (I had said:) Permit me that I cut off his neck. He said: Would you do it if I ordered you? I said: Yes. He said: No, I swear by Allah, this is not allowed for any man after Muhammad (ﷺ).

Abu Dawud said: This is Yazid's version. Ahmad bin Hanbal said: That is, Abu Bakr has no powers to slay a man except for three reasons which the Messenger of Allah (ﷺ) had mentioned: disbelief after belief, fornication after marriage, or killing a man without (murdering) any man by him. The Prophet (ﷺ) had powers to kill.