From Sahih Muslim (Hadith 4388):
Alaqama b. Wa'il reported on the authority of his father that a person was brought to the Messenger of Allah (ﷺ) who had killed another person, and the heir of the person slain had dragged him (to the Holy Prophet) with a strap around his neck. As he turned away Allah's Messenger (ﷺ) said:The killer and the killed are (doomed) to fire. A person came to the other person (the heir of the deceased) and he reported to him the words of the Messenger of Allah (ﷺ), and so he let him off. Isma'il b. Salim said: I made a mention of it to Habib b. Abu Thabit and he said: Ibn Ashwa' reported to me that Allah's Apostle (ﷺ) had asked him to pardon him, but he refused
Reference: Muslim 4388