Islam needs us to make sacrifices for its sake. Just consider what pure and virtuous lives have been sacrificed from the advent of Islam down to the present time. A case in point is Hadrat Amir (Imam Ali) who fought against Muawiyah for eighteen months in the Battle of Siffin, and who killed so many adversaries and lost the lives of so many fellow combatants, over ten thousand people in all, well over this figure. Muawiyah was someone who made claim to being Muslim and to being the Prophet's rightful successor. He prayed at congregational prayer gatherings, was the Friday prayer leader, and so on. He practiced all of the outwardly visible religious practices. Unlike Yazid whose exterior was as aberrant as his interior, Muawiyah was good at keeping up appearances. He kept up appearances and also advocated Islam, so what actually happened to cause Hadrat Amir to engage in battle against him? The reason Imam Ali fought against Muawiyah was because he was a tyrant who had unfairly exploited the people. He had seized Sham from Islamic rule and was forcing the people to behave ruthlessly and to commit injustices. He plundered the people's wealth, the public treasury. Hadrat Amir was obliged by duty to fight against him irrespective of whether he was to be the vanquished or the vanquisher. The fact that he may be defeated if he were to engage in battle at this time, did not concern Hadrat Amir. Once he saw that he was able to confront Muawiyah in battle, he rounded up his troops and battle commenced, although it is true to say that on this particular occasion he was eventually defeated.
Sahifeh, vol.4, Page: 140
Speech, October 25, 1978