The Ismailis are the second largest Shia Muslim community. When Imam Jafar as-Sadiq died in the year 765, a group gave allegiance to his younger son Musa al-Kazim, and after him, in lineal descent, to Muhammad al-Mahdi, their twelfth Imam, who they believe is in hiding and will return to restore order and justice. This group came to the known as the Ithna Asharis, or the Twelvers. The other group gave allegiance to Imam Jafar as-Sadiq’s son Ismail and came to be known as Ismailis.
http://www.iis.ac.uk/view_article.asp?ContentID=104383
The Ismailis have a history that spans 1400 years. As many of you know they belong to the Shia Muslim Community, one of the two major branches of Islam, the Sunni being the other. The Sunni hold that there was no designated successor to the leadership of the Muslim community after the death of Prophet Muhammad. The Shia believe that, although revelation ceased at the Prophet’s death, the need for the community’s spiritual and temporal guidance continued. The authority for this guidance devolved first on Ali, the Prophet’s cousin and son-in-law, and subsequently passed to those male descendants designated in turn…… My responsibilities as a descendant and as the present Imam of the Ismailis concern not only interpretation in matters of faith to a broad diversity of people residing in more than 25 countries, but also relating that faith to the conditions of the present.
— Mawlana Hazar Imam, Royal Society for Asian Affairs, London, United Kingdom, February 6, 1992
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