Narrated Wa'il ibn Hujr:

I was with the Prophet (ﷺ) when a man who was a murderer and had a strap round his neck was brought to him. He then called the legal guardian of the victim and asked him: Do you forgive him? He said: No. He asked: Will you accept the blood-money? He said: No. He asked: Will you kill him? He said: Yes. He said: Take him. When he turned his back, he said: Do you forgive him? He said: No. He said: Will you accept the blood-money? He said: No. He said: Will you kill him? He said: Yes. He said: Take him. After repeating all this a fourth time, he said: If you forgive him, he will bear the burden of his own sin and the sin of the victim. He then forgave him. He (the narrator) said: I saw him pulling the strap.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عُمَرَ بْنِ مَيْسَرَةَ الْجُشَمِيُّ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ عَوْفٍ، حَدَّثَنَا حَمْزَةُ أَبُو عُمَرَ الْعَائِذِيُّ، حَدَّثَنِي عَلْقَمَةُ بْنُ وَائِلٍ، حَدَّثَنِي وَائِلُ بْنُ حُجْرٍ، قَالَ كُنْتُ عِنْدَ النَّبِيِّ صلى الله عليه وسلم إِذْ جِيءَ بِرَجُلٍ قَاتِلٍ فِي عُنُقِهِ النِّسْعَةُ قَالَ فَدَعَا وَلِيَّ الْمَقْتُولِ فَقَالَ ‏"‏ أَتَعْفُو ‏"‏ ‏.‏ قَالَ لاَ ‏.‏ قَالَ ‏"‏ أَفَتَأْخُذُ الدِّيَةَ ‏"‏ ‏.‏ قَالَ لاَ ‏.‏ قَالَ ‏"‏ أَفَتَقْتُلُ ‏"‏ ‏.‏ قَالَ نَعَمْ ‏.‏ قَالَ ‏"‏ اذْهَبْ بِهِ ‏"‏ ‏.‏ فَلَمَّا وَلَّى قَالَ ‏"‏ أَتَعْفُو ‏"‏ ‏.‏ قَالَ لاَ ‏.‏ قَالَ ‏"‏ أَفَتَأْخُذُ الدِّيَةَ ‏"‏ ‏.‏ قَالَ لاَ ‏.‏ قَالَ ‏"‏ أَفَتَقْتُلُ ‏"‏ ‏.‏ قَالَ نَعَمْ ‏.‏ قَالَ ‏"‏ اذْهَبْ بِهِ ‏"‏ ‏.‏ فَلَمَّا كَانَ فِي الرَّابِعَةِ قَالَ ‏"‏ أَمَا إِنَّكَ إِنْ عَفَوْتَ عَنْهُ يَبُوءُ بِإِثْمِهِ وَإِثْمِ صَاحِبِهِ ‏"‏ ‏.‏ قَالَ فَعَفَا عَنْهُ ‏.‏ قَالَ فَأَنَا رَأَيْتُهُ يَجُرُّ النِّسْعَةَ ‏.‏