It was narrated from Ans bin Malik that a man brought the killer of his kinsman to the Messenger of Allah (ﷺ) and the Prophet (ﷺ) said: "Forgive him." But he refused. He said: "Take the Diyah," but he refused. He said: "Go and kill him then, for you are just like him." So he went away, but some people caught up with the man and told him that the Messenger of Allah (ﷺ) had said: "Messenger of Allah had said: "Kill him for you are just like him." So he let him go, and the man passed by me dragging his string.
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عِيسَى بْنُ يُونُسَ، قَالَ حَدَّثَنَا ضَمْرَةُ، عَنْ عَبْدِ اللَّهِ بْنِ شَوْذَبٍ، عَنْ ثَابِتٍ الْبُنَانِيِّ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَجُلاً، أَتَى بِقَاتِلِ وَلِيِّهِ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ النَّبِيُّ صلى الله عليه وسلم " اعْفُ عَنْهُ " . فَأَبَى فَقَالَ " خُذِ الدِّيَةَ " . فَأَبَى قَالَ " اذْهَبْ فَاقْتُلْهُ فَإِنَّكَ مِثْلَهُ " . فَذَهَبَ فَلُحِقَ الرَّجُلُ فَقِيلَ لَهُ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " اقْتُلْهُ فَإِنَّكَ مِثْلَهُ " . فَخَلَّى سَبِيلَهُ فَمَرَّ بِيَ الرَّجُلُ وَهُوَ يَجُرُّ نِسْعَتَهُ .
sunnah.com