Ismailism, known historically as Batiniyya (lit. 'esotericism'), is a denomination of Shia Islam. It is one of the three denominations of Shia Islam, the other two being Twelver Shia Islam and Zaydism. The Ismailis and Zaydis constitute a minority within Shia Islam, in contrast to Twelvers, who constitute the predominant denomination. The Ismailis emphasize a distinction between the exoteric (zahir) and esoteric (batin) dimension of Islam. Unlike the Twelvers, the Ismailis are characterized by a unique emphasis on the esoteric. The Isma'ilis get their name from their acceptance of Isma'il ibn Ja'far as the appointed spiritual successor (Imām) to Ja'far al-Sadiq. The question of succession after al-Sadiq's death divided the early Shia Muslims. The first group accepted the Imamate of his younger son Musa al-Kazim, while the second group considered the Imam to be his eldest son Isma'il, who had predeceased his father. The first and much larger group became known as the Twelvers, while the second and much smaller group came to be known as the Isma'ilis, which separated from the mainstream Shia Islam and formed the Isma'ili sect.
Isma'ili thought is heavily influenced by Neoplatonism. After the death of Muhammad ibn Isma'il in the 8th century CE, the teachings of Ismailism further transformed into the belief system as it is known today, with an explicit concentration on the deeper, esoteric meaning (batin) of the Islamic religion. With the eventual development of Usulism and Akhbarism into the more literalistic (zahir) oriented, Shia Islam developed into two separate directions: the metaphorical Ismaili, Alevi, Bektashi, Alian, and Alawite groups focusing on the mystical path and nature of God, along with the "Imam of the Time" representing the manifestation of esoteric truth and intelligible divine reality, with the more literalistic Usuli and Akhbari groups focusing on divine law (sharia) and the deeds and sayings (sunnah) of Muhammad and the Twelve Imams who were guides and a light to God. The larger sect of Ismaili are the Nizaris, who recognize Aga Khan V as the 50th hereditary Imam, while other groups are known as the Tayyibi sect. The community with the highest percentage of Ismailis is Gorno-Badakhshan, but Isma'ilis can be found in Central Asia, Afghanistan, Iran, Pakistan, Yemen, Lebanon, Malaysia, Syria, India, Saudi Arabia, Jordan, Iraq, Kuwait, East Africa, Angola, Bangladesh, and South Africa, and have in recent years emigrated to Europe, Russia, Canada, Australia, New Zealand, the United States, and Trinidad and Tobago.
Ismailism shares its beginnings with other early Shia sects that emerged during the succession crisis that spread throughout the early Muslim community. From the beginning, the Shia asserted the right of Ali, cousin of Muhammad, to have both political and spiritual control over the community. This also included his two sons, who were the grandsons of Muhammad through his daughter Fatima. The conflict remained relatively peaceful between the partisans of Ali and those who asserted a semi-democratic system of electing caliphs, until the third Rashidun caliph (Uthman) was killed and Ali ascended to the caliphate with popular support.
Soon after his ascendancy, Aisha, the third of Muhammad's wives, claimed, along with Uthman's tribe, the Umayyads, that Ali should take qisas (blood for blood) from the people responsible for Uthman's death. Ali voted against it, as he believed that the situation at the time demanded a peaceful resolution of the matter. Though both parties could rightfully defend their claims, due to escalated misunderstandings, the Battle of the Camel was fought and Aisha was defeated, but was respectfully escorted to Medina by Ali.
Following this battle, Mu'awiya I, the Umayyad governor of Syria, also staged a revolt under the same pretences. Ali led his forces against Mu'awiya until the side of Mu'awiya held copies of the Quran against their spears and demanded that the issue be decided by Islam's holy book. Ali accepted this, and an arbitration was done, which ended in his favor. A group among Ali's army believed that subjecting his legitimate authority to arbitration was tantamount to apostasy, and abandoned his forces. This group, known as the Khawarij, was defeated by Ali before they reached the cities, where they would have been able to blend in with the rest of the population. While he was unable to do this, he nonetheless defeated their forces in subsequent battles.
Regardless of these defeats, the Kharijites survived and became a violently problematic group in Islamic history. After plotting assassinations against Ali, Mu'awiya, and the arbitrator of their conflict, a Kharijite successfully assassinated Ali in 661 CE. The Imāmate then passed to his son Hasan ibn Ali, and later to his son Husayn ibn Ali. According to the Nizari Isma'ili tradition, Hasan was "an Entrusted Imam" (Arabic: الإمام المستودع, romanized: al-imām al-mustawdaʿ), Husayn was the "Permanent Imam" (Arabic: الإمام المستقر, romanized: al-imām al-mustaqar). The Entrusted Imam is an Imam in the full sense except that the lineage of the Imamate must continue through the Permanent Imam. However, the political Caliphate was soon taken over by Mu'awiya, the only leader in the empire at that time with an army large enough to seize control.
Even some of Ali's early followers regarded him as "an absolute and divinely guided leader", whose demands of his followers were "the same kind of loyalty that would have been expected for the Prophet". For example, one of Ali's supporters who also was devoted to Muhammad said to him: "our opinion is your opinion and we are in the palm of your right hand." The early followers of Ali seem to have taken his guidance as "right guidance" deriving from Divine support. In other words, Ali's guidance was seen to be the expression of God's will and the Quranic message. This spiritual and absolute authority of Ali was known as walayah, and it was inherited by his successors, the Imams.
In the 1st century after Muhammad, the term 'sunnah' was not specifically defined as "Sunnah of the Prophet", but was used in connection to Abu Bakr, Umar, Uthman, and some Umayyad Caliphs. The idea of hadith, or traditions ascribed to Muhammad, was not mainstream, nor was hadith criticised. Even the earliest legal texts by Malik b. Anas and Abu Hanifa employ many methods, including analogical reasoning and opinion, and do not rely exclusively on hadith. Only in the 2nd century does the Sunni jurist al-Shafi'i first argue that only the sunnah of Muhammad should be a source of law, and that this sunnah is embodied in hadiths. It would take another one hundred years after al-Shafi'i for Sunni Muslim jurists to fully base their methodologies on prophetic hadiths. Meanwhile, Imami Shia Muslims followed the Imams' interpretations of Islam as normative without any need for hadiths and other sources of Sunni law such as analogy and opinion.
After the death of Imam Hasan, Imam Husayn and his family were increasingly worried about the religious and political persecution that was becoming commonplace under the reign of Mu'awiya's son, Yazid. Amidst this turmoil in 680, Husayn, along with the women and children of his family, upon receiving invitational letters and gestures of support by Kufis, wished to go to Kufa and confront Yazid as an intercessor on behalf of the citizens of the empire. However, he was stopped by Yazid's army in Karbala during the month of Muharram. His family was starved and deprived of water and supplies, until eventually the army came in on the tenth day and martyred Husayn and his companions, and enslaved the rest of the women and family, taking them to Kufa.
This battle would become extremely important to the Shia psyche. The Twelvers as well as Musta'li Isma'ili still mourn this event during an occasion known as Ashura.
The Nizari Isma'ili, however, do not mourn this in the same way because of the belief that the light of the Imam never dies but rather passes on to the succeeding Imām, making mourning arbitrary. However, during commemoration, there are no celebrations in Jama'at Khana during Muharram, and there may be announcements or sessions regarding the tragic events of Karbala. Also, individuals may observe Muharram in a wide variety of ways. This respect for Muharram does not include self-flagellation and beating because they feel that harming one's body is harming a gift from God.