Imam al-Shafi'i (may Allah have mercy on him) said: "It has reached us that Sayyiduna Ali (may Allah be pleased with him) was once delivering a sermon when, in the course of it, he heard the slogan of tahkim (arbitration) from one corner of the mosque: 'There is no judgment except Allah's.'"
Then Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) said: "There is no judgment except Allah's. (This is) a word of truth by which falsehood is intended. You have three rights over us: we will not bar you from the mosques of Allah, that you may remember the name of Allah in them; we will not deprive you of the fay' (state revenue) as long as your hands are with our hands; and we will not be the first to fight you."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / Q16763