سنن أبي داود

Narrated AbuBakr:

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.