سنن النسائي

It was narrated from 'Alqamah bin Wa'il that: his father told them that a man who had killed another man was brought to the Prophet (ﷺ) and he handed him over to their of the victim to kill him. Then the Prophet (ﷺ) said to those who were sitting with him: "The killer and the slain will both be in Fire. "A man went after him and told him that, and when he told him that, he left him (let him go). He (the narrator) said: "I saw him dragging his string when he let him go. I mentioned that the Habib and he said: 'Sa'eed bin Ashwa' told me that the Prophet (ﷺ) commanded the man to forgive him."'