Sunan an-Nasa'i, Volume 5, Book 45, Hadith 4733 (DarusSalam) ⓘ

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 and he handed him over to their of the victim to kill him. Then the Prophet 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 commanded the man to forgive him."'

أَخْبَرَنَا مُحَمَّدُ بْنُ مَعْمَرٍ، قَالَ حَدَّثَنَا يَحْيَى بْنُ حَمَّادٍ، عَنْ أَبِي عَوَانَةَ، عَنْ إِسْمَاعِيلَ بْنِ سَالِمٍ، عَنْ عَلْقَمَةَ بْنِ وَائِلٍ، أَنَّ أَبَاهُ، حَدَّثَهُمْ أَنَّ النَّبِيَّ صلى الله عليه وسلم أُتِيَ بِرَجُلٍ قَدْ قَتَلَ رَجُلاً فَدَفَعَهُ إِلَى وَلِيِّ الْمَقْتُولِ يَقْتُلُهُ فَقَالَ النَّبِيُّ صلى الله عليه وسلم لِجُلَسَائِهِ ‏ "‏ الْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ ‏" ‏ ‏.‏ قَالَ فَاتَّبَعَهُ رَجُلٌ فَأَخْبَرَهُ فَلَمَّا أَخْبَرَهُ تَرَكَهُ ‏.‏ قَالَ فَلَقَدْ رَأَيْتُهُ يَجُرُّ نِسْعَتَهُ حِينَ تَرَكَهُ يَذْهَبُ ‏.‏ فَذَكَرْتُ ذَلِكَ لِحَبِيبٍ فَقَالَ حَدَّثَنِي سَعِيدُ بْنُ أَشْوَعَ قَالَ وَذَكَرَ أَنَّ النَّبِيَّ صلى الله عليه وسلم أَمَرَ الرَّجُلَ بِالْعَفْوِ ‏.‏