Arbitration at Adruh - Mu'awiya opposes Ali
It was decided that the Syrians and the residents of Kufa should nominate an arbitrator each to decide between Ali and Muawiya.
The Syrians choice fell on Amr bin al-A'as who was the rational soul and spokesman of Muawiya. Ali wanted one of his sincere followers like Malik Ashtar or Abdullah bin Abbas to be appointed as an arbitrator for the people of Kufa, but the men of his own army strongly demurred, alleging that men like these two were, indeed, responsible for the war and, therefore, ineligible for that office of trust. They nominated Abu Musa al-Ashari as their arbitrator. Ali found it expedient to agree to this choice in order to ward off bloody dissensions in his army. According to "Asadul Ghaba" (3rd vol., p. 246), Ali had, therefore, taken care to personally explain to the arbitrators, "You are arbiters on condition that you decide according to the Book of God, and if you are not so inclined you should not deem yourselves to be arbiters."
When the arbitrators assembled at Daumet-ul-Jandal, which lay midway between Kufa and Syria and had for that reason been selected as the place for the announcement of the decision, a series of daily meeting was arranged for them to discuss the matters in hand. When the time arrived for taking a decision about the caliphate, Amr bin al-A'as deluded Abu Musa al-Ashari into entertaining the opinion that they should deprive both Ali and Muawiya of the caliphate, and give to the Muslims the right to elect the caliph. Abu Musa al-Ashari also decided to act accordingly. As the time for announcing the verdict approached, the people belonging to both parties assembled. Amr bin al-A'as requested Abu Musa to take the lead in announcing the decision he favoured. Abu Musa al-Ashari agreed to open the proceedings, and said, "We have devised a solution after a good deal of thought and it may put an end to all contention and separatist tendencies. It is this. Both of us remove Ali as well as Muawiya from the caliphate. The Muslims are given the right to elect a new caliph in their places as they think best." As soon as he sat down after giving his award, Amr bin al-A'as sprang to his feet and addressing the gather said, "You have heard Abu Musa who represents Ali. He has deposed Ali from the caliphate. As the representative of Muawiya, I agree with him in the deposition of Ali, but I install Muawiya as the caliph." Here, an disorderly scene ensured in which Abu Musa al-Ashari cursed Amr bin al-A'as. The Syrians hailed the trick played by Amr bin al-A'as as a great diplomatic triumph. It should be noted that the above judgement, the arbitrators did not quote any authority of the Koran or Sunnah to justify deposing Ali.