apostasy) shook the Muslim community in 632–633 AD, immediately after the death of Muhammad. These wars caused the split between the two major sects of Islam: Sunnis and Shias, and numerous deaths on both sides. Sunni and Shia sects of Islam have long accused each other of apostasy. The charge of apostasy dates back to the early history of Islam with the emergence of the Kharijites in the 7th century CE. The original schism between Kharijites, Sunnis, and Shias among Muslims was disputed over the political and religious succession to the guidance of the Muslim community (Ummah) after the death of Muhammad. From their essentially political position, the Kharijites developed extreme doctrines that set them apart from both mainstream Sunni and Shia Muslims. Shias believe ʿAlī ibn Abī Ṭālib is the true successor to Muhammad, while Sunnis consider Abu Bakr to hold that position. The Kharijites broke away from both the Shias and the Sunnis during the First Fitna (the first Islamic Civil War); they were particularly noted for adopting a radical approach to takfīr (excommunication), whereby they declared both Sunni and Shia Muslims to be either infidels (kuffār) or false Muslims (munāfiḳūn), and therefore deemed them worthy of death for their perceived apostasy (ridda). Modern historians recognize that the Christian populations living in the lands invaded by the Arab Muslim armies between the 7th and 10th centuries AD suffered religious persecution, religious violence, and martyrdom multiple times at the hands of Arab Muslim officials and rulers; many were executed under the Islamic death penalty for defending their Christian faith through dramatic acts of resistance such as refusing to convert to Islam, repudiation of the Islamic religion and subsequent reconversion to Christianity, and blasphemy towards Muslim beliefs. Notable Christian converts to Islam who reportedly reverted to Christianity and were executed under the Islamic death penalty for this reason include "Kyros", who was executed by burning in 769 CE, “Holy Elias” in 795 CE, and “Holy Bacchus” in 806 CE. The martyrdoms of forty-eight Christian martyrs that took place in the Emirate of Córdoba between 850 and 859 AD are recorded in the hagiographical treatise written by the Iberian Christian and Latinist scholar Eulogius of Córdoba. The Martyrs of Córdoba were executed under the rule of Abd al-Rahman II and Muhammad I, and Eulogius' hagiography describes in detail the executions of the martyrs for capital violations of Islamic law, including apostasy