Ibn Abbas was asked about a man who killed a believer, then repented, believed, did righteous deeds, and was guided. He replied, "Woe to you, how can he find guidance? I heard your Prophet say, 'The murdered man will come clinging to his murderer, saying, "My Lord, ask this one why he killed me."' By Allah, Allah revealed this verse to your Prophet and did not abrogate it after revealing it."He then said, "Woe to you, how can he find guidance?"
عن ابن عباس انه سئل عن رجل قتل مؤمنا ثم تاب وآمن وعمل صالحا ثم اهتدى قال: ويحك واني له الهدى سمعت نبيكم يقول: يجيء المقتول متعلقا بالقاتل يقول: يا رب سل هذا قتلني؟ والله لقد انزلها الله على نبيكم وما نسخها بعد اذ انزلها قال: ويحك واني له الهدى
Ibn Majah (2621), Nasai (3999), and Ahmad (1941) all narrated it via Sufyan bin Uyayna, from Ammar bin Muawiya Duhni, from Salim bin Abu Jaad, who said, Ibn Abbas was asked, and he mentioned it. Its chain is hasan because of Ammar bin Muawiya Duhni Bajali, for he is hasan al-hadith. It has also been corroborated, as Ibn Abu Asim narrated it in Diyat (33) from Ammar Duhni, pairing him with Yahya Jabir. Moreover, Salim bin Abu Jaad explicitly stated that he heard it directly from Ibn Abbas.The hadith has other routes as well, but what I have mentioned is the soundest of them. Tirmidhi (3029) and Nasai (4005) narrated it by another route, from Warqa bin Umar, from Amr bin Dinar, from Ibn Abbas, in similar wording. Tirmidhi said, "It is a hasan hadith, and some narrated this hadith from Amr bin Dinar, from Ibn Abbas, without making it a raised report (marfu)."