Musnad Ahmed: Hadith 2666

O Ibn 'Abbas, what do you think of a man who kills a believer? Ibn 'Abbas replied: “...his recompense is Hell to abide therein; and the Wrath and the Curse of Allah are upon him, and a great punishment is prepared for him" (an-Nisaʼ 4:93). He said: O Ibn 'Abbas, what do you think if he repents, believes and does righteous deeds? He said: May his mother be bereft of him! How could he repent when the Messenger of Allah (ﷺ) said: "The slain one will come on the Day of Resurrection, carrying his head in his right hand - or he said: in his left hand- and holding on to his killer with his other hand, and with his vein gushing with blood; (he will come) towards the Throne of the Most Merciful, saying, ‘O Lord, ask this one why he killed me’"?