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 and show: "Indeed, God chose Adam and Noah and the family of Abraham and the family of 'Imran over the worlds – (33) Descendants, some of them from others. And God is Hearing and Knowing. (34)" Beliefs and practices Theology Shīʿa Islam is the second largest branch of Islam, followed by 10–15% of all Muslims, considered to be vast and inclusive of many different denominations and subgroups. Shīʿa Islam embodies a completely independent system of religious interpretation and political authority in the Muslim world. The original Shīʿa identity referred to the followers of Imam ʿAlī, and Shīʿa theology was formulated after the hijra (8th century CE). The first Shīʿa governments and societies were established by the end of the 9th century CE. The 10th century CE has been referred to by the scholar of Islamic studies Louis Massignon as "the Shiite Ismaili century in the history of Islam". 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 (: "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 , the "Verse of Wilayah". 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