Musnad Ahmad 1088:1

Bahz narrated to us, Hammad ibn Salamah narrated to us, from Abd al-Malik ibn Umayr, from Rifa'ah ibn Shaddad, who said: I used to stand at the head of al-Mukhtar. When his lying became clear to me, I intended—by Allah—to draw my sword and strike his neck, until I remembered a hadith that Amr ibn al-Hamiq narrated to me. He said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Whoever grants a man security for his life, then kills him, he shall be given the banner of treachery on the Day of Resurrection."