Musannaf Ibn Abi Shayba 38:137

Yazid ibn Harun al-Wasiti narrated to us, he said: Sulayman al-Taymi narrated to us, from Abu Mijlaz, who said: Ali forbade his companions from attacking the Khawarij until they committed an act [of aggression]. They passed by Abdullah ibn Khabbab and seized him. Some of them passed by a date that had fallen from a palm tree, so he took it and put it in his mouth. Some of them said, "A date of a person under a covenant (mu'ahid), so by what [right] did you deem it lawful?" So he threw it out of his mouth. Then they passed by a pig, and one of them poked it with his sword. Some of them said, "A pig of a person under a covenant, so by what [right] did you deem it lawful?" Abdullah [ibn Khabbab] said, "Shall I not guide you to that which is greater in sanctity to you than this?" They said, "Yes." He said, "Myself." So they brought him forward and struck his neck. Ali sent to them, "Surrender to us [the killer of] Abdullah ibn Khabbab." They sent back to him, "And how shall we surrender [the killer] to you when all of us killed him?" He said, "All of you killed him?" They said, "Yes." He said, "Allahu Akbar." Then he ordered his companions to attack them. He said, "Seek them out." He said, "By Allah, ten of you will not be killed, and ten of them will not escape." He said, "So they killed them." He said, "Search among them for Dhu al-Thudayyah." They searched for him and brought him. He said, "Who recognizes him?" They did not find anyone who recognized him, except for a man who said, "I saw him at al-Najaf." Ali said, "He spoke the truth; he is from the Jinn."