سنن النسائي

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 the repentance could avail him! I heard the Prophet (ﷺ) [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.'"