Sunan an-Nasa'i 4722

It was narrated that Abu Hurairah said:"A man was killed during the time of the Messenger of Allah, and the Killer was brought to the Prophet. He handed him over to the heir of the victim, but the killer said: 'O Messenger of Allah, by Allah I did not means to kill him.' The Messenger of Allah said to the next of kin: 'If he is telling the truth and you kill him, you will go to the Fire.' So he let him go. He had been tied with a string and he went out dragging his string, so he became known as Dhul-Nis'ah (the one with the string)