The 'Battle of Siffin' (معركة صفين) was fought in 657 CE (37 AH) between Caliph Ali ibn Abi Talib and the rebellious governor of Syria Mu'awiya ibn Abi Sufyan. The battle is named after its location Siffin on the banks of the Euphrates. The fighting stopped after the Syrians called for arbitration to escape defeat, to which Ali agreed under pressure from some of his troops. The arbitration process ended inconclusively in 658 though it strengthened the Syrians' support for Mu'awiya and weakened the position of Ali. The battle is considered part of the First Fitna and a major step towards the establishment of the Umayyad Caliphate.
The battlefield was located in Siffin, a ruined Byzantine-era village at the right bank of the Euphrates in the vicinity of Raqqa in present-day Syria. It has been identified with the modern village of Abu Hureyra in the Raqqa Governorate.
Ali frequently accused the third caliph, Uthman, of deviating from the Quran and the Sunna, and was joined in his criticism by most of the senior companions of the Islamic prophet Muhammad, including Talha and Zubayr. Uthman was also widely accused of nepotism, corruption, and injustice, and Ali is known to have protested his conduct, including his lavish gifts for his kinsmen, the Umayyads. Ali also protected outspoken companions, such as Abu Dharr al-Ghifari and Ammar ibn Yasir, from Uthman. Ali appears in early sources as a restraining influence on Uthman without directly opposing him. Some supporters of Ali were also part of the opposition to Uthman, joined in their efforts by Talha and Zubayr, and by Aisha, a widow of Muhammad. The last was critical of Uthman for religious innovations and nepotism, but also objected to him for reducing her pension. Among the supporters of Ali were Malik al-Ashtar (657) and other religiously-learned qurra (Quran readers). These wanted to see Ali as the next caliph, though there is no evidence that he communicated or coordinated with them.