Musnad Ahmad 25:824

Yunus narrated to us, Abd al-Wahid narrated to us, Yahya ibn Abd Allah narrated to us, he said: Salim ibn Abi al-Ja’d narrated to us, he said: A man came to Ibn Abbas and said: "O Ibn Abbas, what do you say about a man who killed a believer?" Ibn Abbas said: "His recompense is Hell, wherein he will abide eternally," until the end of the verse. The man said: "O Ibn Abbas, what if he repented, believed, and did righteous deeds?" Ibn Abbas said: "May his mother be bereaved of him! How can there be repentance for him? For the Messenger of Allah (peace and blessings of Allah be upon him) said: 'The murdered person will come on the Day of Resurrection with his head hanging from his right hand—or he said: his left hand—holding his killer with his other hand, his jugular veins gushing blood, until he is before the Throne of the Most Merciful. He will say: "O Lord, ask this one why he killed me."'"