legal opinions in Shīʿa Islam). Twelver Twelver Shīʿīsm or Ithnāʿashariyyah is the largest branch of Shīʿa Islam, and the terms Shīʿa Muslim and Shīʿa often refer to the Twelvers by default. The designation Twelver is derived from the doctrine of believing in twelve divinely ordained leaders, known as "the Twelve Imams". Twelver Shīʿas are otherwise known as Imami or Jaʿfari; the latter term derives from Jaʿfar al-Ṣādiq, the 6th Shīʿīte Imam, who elaborated the Twelver jurisprudence. Twelver Shīʿas constitute the majority of the population in Iran (90%), Azerbaijan (85%), Bahrain (70%), Iraq (65%), and Lebanon (65% of Muslims). Doctrine Twelver doctrine is based on five principles. These five principles known as Usul ad-Din are as follow: Monotheism: God is one and unique; Justice: the concept of moral rightness based on ethics, fairness, and equity, along with the punishment of the breach of these ethics; Prophethood: the institution by which God sends emissaries, or prophets, to guide humankind; Leadership: a divine institution which succeeded the institution of Prophethood. Its appointees (Imams) are divinely appointed; Resurrection and Last Judgment: God's final assessment of humanity. More specifically, these principles are known as Usul al-Madhhab (principles of the Shīʿa branch of Islam) according to Twelver Shīʿas, which differ from Daruriyat al-Din ("Necessities of Religion"), which are principles in order for one to be a Muslim. Daruriyat al-Din don't include leadership (Imamah), as it is not a requirement in order for one to be recognized as a Muslim. However, this category, according to Twelver scholars like Ayatollah Abu al-Qasim al-Khoei, does include belief in God, prophethood, the Day of Resurrection, and other "necessities" (such as the belief in angels). In this regard, Twelver Shīʿas draw a distinction in terms of believing in the main principles of Islam on the one hand, and specifically Shīʿīte doctrines like the Imamate on the other. Books Besides the Quran, which is the sacred text common to all Muslims, Twelver Shīʿas derive scriptural and authoritative guidance from collections of sayings and traditions (ḥadīth) attributed to Muhammad and the Twelve Imams. Below is a list of some of the most prominent of these books: Nahj al-Balagha by Ash-Sharif Ar-Radhi – the most famous collection of sermons, letters & narration attributed to Ali, the first Imam regarded by Shias Kitab al-Kafi by Muhammad ibn Ya'qub al-Kulayni Wasa'il al-Shiʻah by al-Hurr al-Amili The Twelve Imams The Twelve Imams are the spiritual and political