text: Sunni Muslims are the largest denomination of Islam. They are referred to as Ahl ul-Sunna (Arabic: أهل السنة), the folks of the tradition. The word Sunni comes from the word sunna (Arabic : سنة ) which means the tradition of the prophet of Islam Muhammad.\n\nShi'a Islam or Shi`ism (from the Arabic word شيعة, Persian: شیعه) is the second largest denomination of the religion of Islam. Shi'a Muslims adhere to the teachings of the Islamic prophet Muhammad and his Ahlul Bayt (family). Thus, Shi'as reject the rule of the initial three Sunni Caliphs as Sunnis reject the Imamate of the Shi'a Imams. The singular/adjective form is shi`i (Arabic: شيعي.) and refers to a supporter of the Ahlul Bayt and of Ali ibn Abi Talib (Imam Ali) in particular.\n\nSome thirty years after Muhammad's death, the Islamic community plunged into the First Islamic civil war. This civil war led to the emergence of three distinct Islamic groups:\n\nSunnis - Sunnis regard the first four caliphs (Abu Bakr, Umar ibn al-Khattab, Uthman, and Ali) as Rightly Guided Caliphs, that is, caliphs who ruled in accordance with the Qur'an and the sunnah, or way of Muhammad and Sunni reject the Shia Imams. Sunnis believe that most of the succeeding caliphs failed to live up to these standards. In spite of these failures on the part of the secular leadership, the Sunni clergy (the ulema) counseled believers to submit to the authorities; this was better than constant community strife. The full name of the Sunni branch is Ahl al-Sunna wa al-Jama'ah. \nShi'a - Shi'a regard Imam Ali as the first Imam and generally reject the first three sunni's caliphates, believing that his was the only "Rightly Guided" caliphate, and that only the Imams of the household and descendants of Muhammad have the right to rule. Shi'as and a handful of Sunni scholars accepted Hasan ibn Ali's claim as caliph, though historical consensus states that Hasan Have ruled for six months.The Salafis (or the Early Muslims), do not accept the Shi'a as Muslims. \n\nThis was the third group:\n\nKhwarij, or Kharijites - The Khwarij were initially loyal to Ali ibn Abi Talib, the fourth caliph, but turned against him after he accepted arbitration during the First Islamic civil war. Because the Khwarij had a very narrow view of what constitutes kufr (acts that invalidate one's Islam), they quickly split up into sects within themselves, each accusing one another of having fallen into disbelief. Though one branch of the Khwarij survives in Yemen and Oman as the Ibadi denomination of Islam, Khwarij doctrine has been largely rejected and relegated to the history books. \nOther divisions have arisen since the civil war of the 7th century CE. Some groups are now extinct. Of the existing groups, Sunni Muslims do not accept members of the Nation of Islam, Ahmadiyya, and Zikri as fellow Muslims.