Musnad Ahmad 1088:2

Ibn Numayr narrated to us, 'Isa al-Qari' Abu 'Umar narrated to us, al-Suddi narrated to me, from Rifa'ah al-Fityani, who said: I entered upon al-Mukhtar. He said: So he threw a cushion for me and said: "Were it not that my brother Gabriel stood up from this, I would have thrown it to you." He said: So I wanted to strike his neck, but I remembered a hadith that my brother 'Amr ibn al-Hamiq had narrated to me. He said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Any believer who grants security to a believer regarding his blood, then kills him, I am innocent of the killer."