The root cause for lack of unity among Muslims is their lack of patience. Muslims make a huge hue and cry about every occasion of difference among them. The conquest of Iran was a very important event in Muslim history. The Iranians were very powerful compared to the Muslims. The battle at Qadsiya was very crucial in this conquest. The Muslim commander in this battle was Sad ibn Abi Waqqas. During battle he sat on the terrace of an abandoned fort. He did not directly participate in the war, but only observed the Muslim army fighting in front of him. This led to many complaints among the Muslims who took part in the battle. One of the Muslims said that the wives of many of the Muslim fighters were widowed as their husbands died fighting, but Sad's wife did not become a widow. This shows the deep complaint Muslims at Qadsiya had developed with regard to their commander Sad. In spite of this complaint, the Muslims fought very valiantly and defeated the powerful Iranian army. Sad had kept it secret that he had been suffering from an illness which obstructed movement. This is why he sat atop the fort and did not participate in battle. The Muslims fought with unity in spite of the misgivings they had developed for Sad, although this misgiving was unfounded because Sad had a justified reason for what he did. Unity comes when people in a group can tolerate differences. The only condition for unity is patience. If there is no patience in members of a group, there can be no unity within the group. Without unity, a group is utterly powerless.