Musannaf Ibn Abi Shayba 38:174

Ibn Numayr narrated to us, from al-Ajalih, from Salamah ibn Kuhayl, from Kathir ibn Nimr, who said: While I was at the Friday prayer and Ali ibn Abi Talib was on the pulpit, a man came and said, "There is no judgment except for Allah." Then another stood up and said, "There is no judgment except for Allah." Then they stood up from the corners of the mosque, invoking the judgment of Allah. He gestured with his hand, "Sit down. Yes, 'There is no judgment except for Allah' is a statement of truth by which falsehood is sought. The judgment of Allah is awaited among you." "Now, you have three things from me: As long as you are with us, we will not prevent you from the mosques of Allah, that His name be mentioned in them; and we will not prevent you from the spoils of war as long as your hands are with our hands; and we will not fight you until you fight." Then he resumed his sermon.