He became a Muslim in the time of the Prophet [s].
He became a Muslim in the time of the Prophet [s]. He was loyal to his Islam. He took part and fought bravely in the Battle of Yarmook. He had brave attitudes in stopping the Romans' attacks against the Muslim Army. So, his eye was split by a sword, namely, its lower lid was split. Thus, he was called al-Ashtar. In 30 A.H., the Muslims in Kufa and other Muslim cities were angry with their rulers' behaviour.
For example, al-Waleed bin Akabah, the Caliph Uthman's brother, the ruler of Kufa, behaved contrary to Islam - he drank alcohol and spent his time in amusements. One day, al-Waleed entered mosque drunk. He prayed four Raka'as during the morning prayers. Then he turned to the worshipers and said sarcastically: Shall I increase my prayers? People were displeased with his behaviour. They criticized him in markets, houses and mosques.
People asked each other: Has not the Caliph found a good ruler to replace this bad one? He drank alcohol openly. He violated the teachings of the religion and the Muslims' rights. So, people thought about a way to solve the problem. Finally, they decided to ask the advice of the good people. So, they went to Malik al-Ashtar. Malik al-Ashtar said to them: First we'd better advise him. Then we'll tell the Caliph about his bad behaviour. Malik and some good people went to the ruler's palace.
When they got into the palace, they saw him drinking as usual. They advised him to behave well. But he scolded and dismissed them. So, they decided to go to al-Madina al-Munawwara to meet the Caliph and to tell him about the problem. The delegation met the Caliph and told him about his ruler's bad behaviour. It was unfortunate that he scolded and dismissed them. Besides, he refused to hear their complaints. So, they became disappointed.
They thought about going to Ali bin Abu-Talib, our Master Muhammad's cousin, because he was the only hope to reform the situation. The Delegation In the meantime, all people all over the Muslim cities complained of the rulers' bad behaviour. The companions went to Imam Ali's house. They told him about the rulers' persecution and corruption. Imam Ali [a] was sad to hear that. So, he went to the Caliph's palace.
He met Uthman and advised him: Uthman, the Muslims are complaining of the rulers' persecution. And you know that very well I've heard Allah's Apostle [s] saying: "On the Day of Judgement, the unjust imam will be brought to hell. And no one will support or excuse him. Then, he will be thrown into hell.