A man who had killed someone was brought to the Messenger of Allah, and he was brought by the heir of the victim. The Messenger of Allah said to him. 'Will you forgive him? He said: No.' He said: 'Will you kill him? He said: 'Yes.' He said: 'Go away.' Then when he went away, he called him back and said: will you forgive him?' He said: 'No.' He said: 'Will you accept the Diyah? He said: 'No.' He said: 'will you kill him? He said: 'Yes.' He said: 'Go away.' Then when he had gone he said: If you forgive him, he will carry your sin and the sin of your companion (the victim)." So he forgave him and let him go." He said: "And I saw him dragging his string." (Using translation from Nasāʾī 4723)   

جِيءَ بِالْقَاتِلِ الَّذِي قَتَلَ إِلَى رَسُولِ اللهِ ﷺ جَاءَ بِهِ وَلِيُّ الْمَقْتُولِ فَقَالَ لَهُ رَسُولُ اللهِ ﷺ أَتَعْفُو؟ قَالَ لَا قَالَ أَتَأْخُذُ الدِّيَةَ؟ قَالَ لَا قَالَ أَتَقْتُلُ؟ قَالَ نَعَمْ قَالَ فَاذْهَبْ بِهِ فَلَمَّا ذَهَبَ دَعَاهُ فَقَالَ أَمَا إِنَّكَ إِنْ عَفَوْتَ عَنْهُ فَإِنَّهُ يَبُوءُ بِإِثْمِكَ وَإِثْمِ صَاحِبِكَ فَعَفَا عَنْهُ فَأَرْسَلَهُ قَالَ فَرَأَيْتُهُ وَهُوَ يَجُرُّ نِسْعَتَهُ  

[Machine] The Prophet Muhammad ﷺ said, "Whoever intentionally kills someone, the decision is left to the guardian of the deceased: if he wishes, he can choose to have the killer executed, or if he wishes, he can choose to accept blood money (compensation)."  

قَالَ النَّبِيُّ ﷺ مَنْ قَتَلَ عَمْدًا دُفِعَ إِلَى وَلِيِّ الْمَقْتُولِ فَإِنْ شَاءَ قَتَلَهُ وَإِنْ شَاءَ أَخَذَ الدِّيَةَ