Sunan an-Nasa'i, Book 45, Hadith 161 (In-Book) ⓘ

It was narrated from Salim bin abi Ja'd that: Ibn 'Abbas was asked about someone who killed a believer deliberately then he repented, believed and did righteous deeds, and followed true guidance. Ibn 'Abbas said: "There is no way he could repent! I heard your Prophet say; He (the victim) will come hanging onto his killer with his jugular veins flowing with blood and saying: "Ask him why he killed me." Then he said: "by Allah, Allah revealed it and never abrogated anything of it.

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عَمَّارٍ الدُّهْنِيِّ، عَنْ سَالِمِ بْنِ أَبِي الْجَعْدِ، أَنَّ ابْنَ عَبَّاسٍ، سُئِلَ عَمَّنْ قَتَلَ مُؤْمِنًا مُتَعَمِّدًا ثُمَّ تَابَ وَآمَنَ وَعَمِلَ صَالِحًا ثُمَّ اهْتَدَى فَقَالَ ابْنُ عَبَّاسٍ وَأَنَّى لَهُ التَّوْبَةُ سَمِعْتُ نَبِيَّكُمْ صلى الله عليه وسلم يَقُولُ ‏ "‏ يَجِيءُ مُتَعَلِّقًا بِالْقَاتِلِ تَشْخَبُ أَوْدَاجُهُ دَمًا يَقُولُ سَلْ هَذَا فِيمَ قَتَلَنِي ‏" ‏ ‏.‏ ثُمَّ قَالَ وَاللَّهِ لَقَدْ أَنْزَلَهَا وَمَا نَسَخَهَا ‏.‏