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 the repentance could avail him! I heard the Prophet [SAW] say: 'He (the victim) will come hanging onto his killer, with his jugular veins flowing with blood and saying: O Lord, ask him why he killed me. Then he said: By Allah, Allah revealed it and never abrogated anything of it.'" (Using translation from Nasāʾī 3999)
سَمِعْتُ نَبِيَّكُمْ ﷺ يَقُولُ يَجِيءُ مُتَعَلِّقًا بِالْقَاتِلِ تَشْخَبُ أَوْدَاجُهُ دَمًا فَيَقُولُ أَيْ رَبِّ سَلْ هَذَا فِيمَ قَتَلَنِي؟ ثُمَّ قَالَ وَاللهِ لَقَدْ أَنْزَلَهَا اللهُ ثُمَّ مَا نَسَخَهَا