The Ibadi movement or Ibadism (al-ʾIbāḍiyya, alʔibaːˈdʕijja) is a school of Islam. It has been called by some the third branch of Islam, along with Sunni Islam and Shia Islam. The followers of Ibadism are known as the Ibadis. Ibadism emerged around 60 years after the Islamic prophet Muhammad's death in 632 AD as a moderate school of the Khawarij movement, although contemporary Ibāḍīs strongly object to being classified as Kharijites. Ibadism is currently the largest Muslim denomination in Oman, but is also practised to a lesser extent in Algeria (Mzab), Tunisia (Djerba), Libya (Nafusa), and Tanzania (Zanzibar). Throughout Islamic history, particularly under the Umayyads and the Almoravids, and continuing to the modern era, Ibadis have faced religious persecution in the Muslim world. Kharijites The Ibadis emerged as a moderate school of the Kharijites, an Islamic sect that originated from the Muhakkima (محكمة) and al-Haruriyya (الحرورية). The Muhakkima and al-Haruriyya were supporters of Ali in the First Fitna who abandoned the Alid cause after rejecting arbitration between Ali and Mu'awiya I at the Battle of Siffin in 657 CE. Following the Battle of Siffin, the Kharijites became involved in almost constant conflict with supporters of both the Alids and Umayyads. The Kharijites were organised inside major Muslim settlements, often becoming involved in local rebellions against Umayyad authorities. After the Second Fitna commenced in 680 CE, the Kharijites gradually split into four principal groups (usul al-Khawarij) of varying levels of moderation and extremism. The Ibadi school emerged as a moderate grouping in Basra, based on the teachings of Abdallah ibn Ibad of the Banu Tamim, who was recognised, perhaps posthumously, as imam by his followers. The Ibadi school of Kharijites traces its origins to the aftermath of the siege of Mecca in 683 CE. Abd Allāh ibn Ibāḍ was one of a group of Basran Kharijites who, under the leadership of Nafi ibn al-Azraq, joined the defenders of the city of Mecca fighting against the Umayyads in the early stages of the second Muslim civil war.