Musannaf Ibn Abi Shayba 18:1029

Abu Bakr narrated to us, he said: Yazid ibn Harun narrated to us, he said: Abu Malik al-Ashja‘i informed us, from Sa‘d ibn ‘Ubaydah, he said: A man came to Ibn ‘Abbas and said: "Is there repentance for one who kills a believer?" He said: "No, except the Fire." When he left, his companions said to him: "You did not used to give us this fatwa. You used to give us the fatwa that there is an accepted repentance for one who kills a believer, so what is the matter today?" He said: "I think he is an angry man who wants to kill a believer." He said: So they sent someone after him, and they found him to be as such.