Thabit (may Allah have mercy on him) narrates from Sayyiduna Anas (may Allah be pleased with him) concerning the story of the Qurra' and the martyrdom of Sayyiduna Haram bin Milhan (may Allah be pleased with him); at the end of it he says: After that, Sayyiduna Abu Talhah (may Allah be pleased with him) said to me: What do you think about the killer of Haram? I said: What is his state? Allah has done with him what He has done. He said: He has become a Muslim; do not do anything (against him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18194