Musannaf Ibn Abi Shayba 38:144

Yahya ibn Adam narrated to us, he said: Ibn Idris narrated to us, from Isma’il ibn Sami’ al-Hanafi, from Abu Razin, who said: When the arbitration took place at Siffin and the Khawarij separated from Ali, they returned having separated from him, while they were in a camp and Ali was in a camp, until Ali entered Kufa with the people and his camp, and they went to Harura’ with their camp. Ali sent Ibn Abbas to them, and he spoke to them, but it did not have an effect on them. Then Ali went out to them and spoke to them until they and he agreed upon contentment, so they returned until they entered Kufa in a state of contentment from him and from them. They stayed for two days or thereabouts. He said: Then al-Ash’ath ibn Qays entered—and he used to enter upon Ali—and he said: "The people are saying that you have returned to them regarding their disbelief (or: hatred)." When the next day, Friday, came, he ascended the pulpit, praised Allah and extolled Him, then he delivered a sermon and mentioned them, their separation from the people, and the matter in which they had departed from him, and he criticized them and criticized their affair. He said: When he descended from the pulpit, they called out from the corners of the mosque: "There is no judgment except for Allah." Ali said: "I await the judgment of Allah regarding you." Then he gestured with his hand like this, silencing them with the gesture while he was on the pulpit, until a man among them came, placing his two fingers in his ears, while he was saying: "If you associate partners with Allah, your deeds will surely be rendered void, and you will surely be among the losers."