Shia Islam significant person Alī ibn Abī Ṭālib
Terminology
Collectively, adherents of Shīʿa Islam are called the Shīʿa (Arabic: شِيعَة; Arabic pronunciation: [ˈʃiːʕa]), which is short for Shīʿatu ʿAlī (Arabic: شِيعَة عَلِيّ; [ˈʃiːʕatu ˈʕaliː]) meaning "followers of Ali", "faction of Ali", or "partisans of Ali"; Shīʿī (شِيعِيّ [ˈʃiːʕiː]) denotes both the singular noun and the adjective form, while Shīʿiyyūn (شِيعِيُّون [ʃiːʕijˈjuːn]) refers to the plural noun. Shīʿa or Shia and Shīʿism/Shīʿite or Shiism/Shiite are the forms used in English and other European languages for adherents, mosques, traditions, and things associated with the Shīʿa branch of Islam.The term was first used during Muhammad's lifetime. At present, the word refers to the Muslims who believe that the leadership of the Muslim community after Muhammad belongs to ʿAlī ibn Abī Ṭālib, Muhammad's cousin and son-in-law, and his successors. Nawbakhti states that the term Shīʿa refers to a group of Muslims who at the time of Muhammad and after him regarded ʿAlī as the Imam and caliph. Al-Shahrastani expresses that the term Shīʿa refers to those who believe that ʿAlī is designated as the heir, Imam, and caliph by Muhammad and that ʿAlī's authority is maintained through his descendants. For the adherents of Shīʿa Islam, this conviction is implicit in the Quran and the history of Islam. Shīʿa Muslim scholars emphasize that the notion of authority is linked to the family of the Abrahamic prophets as the Quranic verses  3:33 and  3:34 show: "Indeed, Allah chose Adam, Noah, the family of Abraham, and the family of ’Imrân above all people ˹of their time˺. They are descendants of one another. And Allah is All-Hearing, All-Knowing."Profession of faith (Shahada)
The Shīʿa version of the Shahada, the Islamic profession of faith, differs from that of the Sunnīs. The Sunnī version of the Shahada states "There is no god except God, Muhammad is the messenger of God", but to this declaration of faith Shīʿa Muslims append the phrase Ali-un-Waliullah (علي ولي الله: "ʿAlī is the Wali (custodian) of God"). The basis for the Shīʿa belief in ʿAlī ibn Abī Ṭālib as the Wali of God is derived from the Quranic verse  5:55.
This additional phrase to the declaration of faith embodies the Shīʿa emphasis on the inheritance of authority through Muhammad's family and lineage. The three clauses of the Shīʿa version of the Shahada thus address the fundamental Islamic beliefs of Tawḥīd (unity and oneness of God), Nubuwwah (the prophethood of Muhammad), and Imamah (the Imamate, leadership of the faith).Infallibility (Ismah)
Ismah is the concept of infallibility or "divinely bestowed freedom from error and sin" in Islam. Muslims believe that Muhammad, along with other prophets and messengers in Islam, possessed ismah. Twelver and Ismāʿīlī Shīʿa Muslims also attribute the quality to Imams as well as to Fāṭimah, daughter of Muhammad, in contrast to the Zaydī Shīʿas, who do not attribute ismah to the Imams. Though initially beginning as a political movement, infallibility and sinlessness of the Imams later evolved as a distinct belief of (non-Zaydī) Shīʿīsm.According to Shīʿa Muslim theologians, infallibility is considered a rational, necessary precondition for spiritual and religious guidance. They argue that since God has commanded absolute obedience from these figures, they must only order that which is right. The state of infallibility is based on the Shīʿa interpretation of the verse of purification. Thus, they are the most pure ones, the only immaculate ones preserved from, and immune to, all uncleanness. It does not mean that supernatural powers prevent them from committing a sin, but due to the fact that they have absolute belief in God, they refrain from doing anything that is a sin.They also have a complete knowledge of God's will. They are in possession of all knowledge brought by the angels to the prophets (nabī) and the messengers (rāsūl). Their knowledge encompasses the totality of all times. Thus, they are believed to act without fault in religious matters. Shīʿa Muslims regard ʿAlī ibn Abī Ṭālib as the successor of Muhammad not only ruling over the entire Muslim community in justice, but also interpreting the Islamic faith, practices, and its esoteric meaning. ʿAlī is regarded as a "perfect man" (al-insan al-kamil) similar to Muhammad, according to the Shīʿa viewpoint.History
Succession of ʿAlī
Shīʿa Muslims believe that just as a prophet is appointed by God alone, only God has the prerogative to appoint the successor to his prophet. They believe God chose ʿAlī ibn Abī Ṭālib to be Muhammad's successor, infallible, the first caliph (khalīfa, head of state) of Islam. Shīʿa Muslims believe that Muhammad designated Ali as his successor by God's command (Eid Al Ghadir). ʿAlī was Muhammad's first-cousin and closest living male relative as well as his son-in-law, having married Muhammad's daughter, Fāṭimah.The Party of ʿAlī
Even during the time of Muhammad, there were signs of split among the companions with Salman al-Farsi, Abu Dharr al-Ghifari, Miqdad, and Ammar ibn Yasir amongst the most vehement and loyal supporters of ʿAlī.Imamate of the Ahl al-Bayt
Later, most denominations of Shīʿa Islam, including Twelvers and Ismāʿīlīs, became Imamis. Imami Shīʿītes believe that Imams are the spiritual and political successors to Muhammad. Imams are human individuals who not only rule over the Muslim community with justice, but also are able to keep and interpret the divine law and its esoteric meaning. The words and deeds of Muhammad and the Imams are a guide and model for the community to follow; as a result, they must be free from error and sin, and must be chosen by divine decree (nass) through Muhammad. According to this view peculiar to Shīʿa Islam, there is always an Imam of the Age, who is the divinely appointed authority on all matters of faith and law in the Muslim community. ʿAlī was the first Imam of this line, the rightful successor to Muhammad, followed by male descendants of Muhammad through his daughter Fatimah.This difference between following either the Ahl al-Bayt (Muhammad's family and descendants) or pledging allegiance to Abū Bakr has shaped the Shīʿa—Sunnī divide on the interpretation of some Quranic verses, ḥadīth literature (accounts of the sayings and living habits attributed to the Islamic prophet Muhammad during his lifetime), and other areas of Islamic belief throughout the history of Islam. For instance, the ḥadīth collections venerated by Shīʿa Muslims are centered on narrations by members of the Ahl al-Bayt and their supporters, while some ḥadīth transmitted by narrators not belonging to or supporting the Ahl al-Bayt are not included. Those of Abu Hurairah, for example, Ibn Asakir in his Taʿrikh Kabir, and Muttaqi in his Kanzuʿl-Umma report that ʿUmar ibn al-Khaṭṭāb lashed him, rebuked him, and forbade him to narrate ḥadīth from Muhammad. ʿUmar is reported to have said: "Because you narrate hadith in large numbers from the Holy Prophet, you are fit only for attributing lies to him. (That is, one expects a wicked man like you to utter only lies about the Holy Prophet.) So you must stop narrating hadith from the Prophet; otherwise, I will send you to the land of Dus." (An Arab clan in Yemen, to which Abu Hurairah belonged). According to Sunnī Muslims, ʿAlī was the fourth successor to Abū Bakr, while Shīʿa Muslims maintain that ʿAlī was the first divinely sanctioned "Imam", or successor of Muhammad. The seminal event in Shīʿa history is the martyrdom at the Battle of Karbala of ʿAlī's son, Ḥusayn ibn ʿAlī, and 71 of his followers in 680 CE, who led a non-allegiance movement against the defiant caliph.