First Fitna: Battle of Siffin

On July 26, 657, the Battle of Siffin began during the first Muslim civil war between Ali ibn Abi Talib and Muawiyah I near the Euphrates River. From the article:

"Battle of Siffin - Background:
Following the murder of Caliph Uthman ibn Affan, the caliphate of the Muslim Empire passed to the cousin and son-in-law of the Prophet Muhammad, Ali ibn Abi Talib. Shortly after ascending to the caliphate, Ali commenced consolidating his hold over the empire. Among those who opposed him was the governor of Syria, Muawiyah I. A kinsman of the slain Uthman, Muawiyah refused to acknowledge Ali as caliph due his inability to bring the murders to justice. In an attempt to avoid bloodshed, Ali sent an envoy, Jarir, to Syria to seek a peaceful solution. Jarir reported that Muawiyah would submit when the murderers were caught.

Battle of Siffin - Muawiyah Seeks Justice:
With the blood-stained shirt of Uthman hanging in the Damascus mosque, Muawiyah's large army marched out to meet Ali, pledging not to sleep at home until the murderers were found. After first planning to invade Syria from the north Ali instead elected to move directly across the Mesopotamian desert. Crossing the Euphrates River at Riqqa, his army moved along its banks into Syria and first spotted his opponent's army near the plain of Siffin. After a small battle over Ali's right to take water from the river, the two sides pursued a final attempt at negotiation as both wished to avoid a major engagement. After 110 days of talks, they were still at an impasse. On July 26, 657, with the talks over, Ali and his general, Malik ibn Ashter, began a massive attack on Muawiyah's lines.

Battle of Siffin - A Bloody Stalemate:
Ali personally led his Medinan troops, while Muawiyah watched from a pavilion, preferring to let his general Amr ibn al-Aas, direct the battle. At one point, Amr ibn al-Aas shattered part of the enemy line and nearly broke through far enough to kill Ali. This was countered by a massive attack, led by Malik ibn Ashter, which nearly forced Muawiyah to flee the field and badly reduced his personal bodyguard. The fighting continued for three days with neither side gaining an advantage, though Ali's forces were inflicting a larger number of casualties. Concerned that he might lose, Muawiyah offered to settle their differences through arbitration.

Battle of Siffin - Aftermath:
The three days of fighting had cost Muawiyah's army approximately 45,000 casualties to 25,000 for Ali ibn Abi Talib. On the battlefield, the arbitrators decided that both leaders were equals and the two sides withdrew to Damascus and Kufa. When the arbitrators met again in February 658, no resolution was achieved. In 661, following the assassination of Ali, Muawiyah ascended to the caliphate, reuniting the Muslim Empire. Crowned in Jerusalem, Muawiyah established the Umayyad caliphate, and began working to expand the state. Successful in these endeavors, he reigned until his death in 680."