When he went to Basrah as governor of the city, he called the inhabitants to a meeting and addressed them: "The Amir al-Muminin, Umar, has sent me to you to teach you the Book of your Lord and the Sunnah of His Prophet and to clean your streets for you." People were taken aback when they heard these words. They could easily understand that one of the responsibilities of a Muslim ruler was to instruct people in their religion. However, that one of his duties should be to clean streets was something new and surprising to them. Who was this governor of whom the Prophet's grandson, al-Hasan, may God be pleased with him said: "There was no rider who came to Basrah who was better for its people than he." His real name was Abdullah ibn Qays but he was and continues to be known as Abu Musa al-Ashari. He left his native land, the Yemen, for Makkah immediately after hearing that a Prophet had appeared there who was a man of rare insight, who called people to the worship of One God and who insisted on the highest standards of morality.
At Makkah, he stayed in the company of the Prophet and gained knowledge and guidance. He returned to his country to propagate the word of God and spread the mission of the noble Prophet, peace be on him. We have no further news of him for more than a decade. Then just after the end of the Khaybar expedition he came to the Prophet in Madinah. His arrival there coincided with that of Jaffar ibn Abi Talib and other Muslims from Abyssinia and the Prophet welcomed them all with joy and happiness. This time Abu Musa did not come alone. He came with more than fifty persons from the Yemen all of whom had accepted Islam. Among them were his two brothers, Abu Ruhm and Abu Burdah. The Prophet referred to the whole group as the "Asharis". In fact he sometimes referred to all Yemenis as Asharis after Abu Musa al-Ashari. He often praised the group for their soft and tender-hearted nature and held them up to the rest of his companions as a high example of good behavior. He once said of them: "If the Asharis go on an expedition or if they only have a little food among them, they would gather all they have on one cloth and divide it equally among themselves. They are thus from me and I am from them." Abu Musa soon became highly esteemed in the Muslim community. He had many great qualities. He was a faqih endowed with intelligence and sound judgement and was ranked as one of the leading judges in the early Muslim community. People used to say: "The judges in this ummah are four: Umar, Ali, Abu Musa and Zayd ibn Thabit."
Abu Musa had a natural, uncomplicated disposition. He was by nature a trusting person and expected people to deal with him on the basis of trust and sincerity. In the field of jihad, he was a warrior of great courage and endurance and skill. The Prophet said of him: "The master of horsemen is Abu Musa." "Abu Musa's insight and the soundness of his judgment did not allow him to be deceived by an enemy in battle. In battle conditions he saw situations with complete clarity and executed his actions with a firm resolve. Abu Musa was in command of the Muslim army traversing the lands of the Sasanian Empire. At Isfahan, the people came to him and offered to pay the jizyah (in return for military protection) to make peace and avoid fighting. However. they were not sincere in their offer and merely wanted an opportunity to mount a treacherous attack on the Muslims. Abu Musa however saw through their real intentions and he remained on the alert. Thus when the Isfahanis launched their attack, the Muslim leader was not caught off-guard, He engaged them in battle and before midday of the following day, he had won a decisive victory.
In the major campaigns against the powerful Sasanian Empire Abu Musa's role was outstanding. In the great Battle of Tustar itself, he distinguished himself as a military commander. The Persian commander, Hormuzan, had withdrawn his numerous forces to the strongly fortified city of Tustar. The Caliph Umar did not underestimate the strength of the enemy and he mobilized powerful and numerous force to confront Hormuzan. Among the Muslim forces were dedicated veterans like Ammar ibn Yasir, al-Baraa ibn Malik and his brother Anas, Majra'a al-Bakri and Salamah ibn Rajaa. Umar appointed Abu Musa as commander of the army. So well fortified was Tustar that it was impossible to take it by storm. Several attempts were made to breach the walls but these proved unsuccessful. There followed a long and difficult siege which became even more testing and agonizing for the Muslims when, as we saw in the story of al-Baraa ibn Malik, the Persians began throwing down iron chains from the walls of the fortress at the ends of which were fastened red-hot iron hooks. Muslims were caught by these hooks and were pulled up either dead or in the agony of death. Abu Musa realized that the increasingly unbearable impasse could only be broken by a resort to stratagem. Fortunately, at this time a Persian defected to the Muslim side and Abu Musa induced him to return behind the walls of the fortified city and use whatever artful means he could to open the city's gates from within. With the Persian he sent a special force of hand-picked men. They succeeded well in their task, opened the gates and made way for Abu Musa's army. Within hours the Persians were subdued.
In spite of the fact that Abu Musa was a strong and powerful warrior, he often left the battlefield transformed into a penitent, weeping person. At such times, he would read the Quran in a voice that profoundly stirred the souls of all who listened to him. Concerning his moving and melodious recitation of the Quran the Prophet, peace be on him, had said: "Abu Musa has indeed been given one of the flutes of the people of David." Also, Umar, may god be pleased with him, often summoned Abu Musa and asked him to recite from the Book of God, saying: "Create in us a yearning for our Lord, O Abu Musa." As a mark of his dedication to the Quran, Abu Musa was one of the few companions who had prepared a mushaf a written collection of the revelations. Abu Musa only participated in fighting against the armies of Mushrikin, armies which tried to oppose the religion of God and extinguish the light of faith. When fighting broke out among Muslims, he fled from such conflict anti never look any part in it. Such was his stand in the conflict that arose between Ali and Muawiyah. It is in relation to this conflict and in particular his role as an adjudicator that the name of Abu Musa al-Ashari is most widely known.
Briefly, Abu Musa's position appeared to be that of a 'neutral.' He saw Muslims killing each other and felt that if the situation were to continue the very future of the Muslim ummah would be threatened. To start off with a clean slate. the Khalifah Ali should give up the position and Muawiyah should relinquish any claim to be Khalifah and the Muslims should be given a free choice to elect whoever they wanted as Khalifah. It was of course true that Imam Ali held the position of Khalifah legitimately and that any unlawful revolt could only have as its object the challenging and overturning of the rule of law. However, developments had gone so far, the dispute had become so bloody and there seemed to be no end in sight except further bloodshed, that a new approach to a solution seemed the only hope of avoiding further bloodshed and continuous civil war. When Imam Ali accepted the principle of arbitration, he wanted Abdullah ibn Abbas to represent him. But an influential section of his followers insisted on Abu Musa. Their reason for so doing was that Abu Musa had not taken part in the dispute from its beginning. Instead he had kept aloof from both parties when he despaired of bringing about an understanding and a reconciliation and putting an end to the fighting. Therefore, they felt, he was the most suitable person to be the arbitrator.
Imam Ali had no reason to doubt the devotion of Abu Musa to Islam and his truthfulness and sincerity. But he knew the shrewdness of the other side and their likely resort to ruses and treachery. He also knew that Abu Musa in spite of his understanding and his knowledge despised deceit and conspiracies and always wanted to deal with people on the basis of trust and honesty, not through cunning. Ali therefore feared that Abu Musa would be deceived by others and that arbitration would end up with the victory of guile over honesty and that the situation would end up being more perilous than it was. Adjudication nonetheless began with Abu Musa representing the side of Ali and Amr ibn al-Aas representing the side of Muawiyah. A possible version of their historic conversation has been recorded in the book "Al-Akhbar at-Tiwal" by Abu Hanifah Ad-Daynawawi