In Twelver Shia Islam, the Major Occultation (, ) (329 AH–present; 941 CE–present) is the second occultation of the Hidden Imam, Muhammad al-Mahdi, which is expected to continue until his rise at the end times to establish peace and justice on earth. Although Sunni and Shia Muslims differ slightly in their interpretation of him, most Muslims believe in the figure of Mahdi owing to the numerous prophetical traditions in canonical Sunni and Shia hadith mentioning him.

The Major Occultation began in 329 AH (941 CE) with the death of the fourth successive agent of the Hidden Imam, Abu al-Hasan al-Samarri, marking the end of the Minor Occultation (260-329 AH, 874-941 CE). Shortly before his death, al-Samarri received a letter from the Hidden Imam, which predicted his imminent death, ordered him not to designate a successor, and announced the beginning of the complete occultation, in which there would be no agent. He is believed by Twelver Shia Muslims to remain responsible for the affairs of men and their inward spiritual guidance during the occultation.

The concept of occultation was already present among Muslims in the 7th century since the Kaysanites who believed Muhammad ibn al-Hanafiyya was the Mahdi. After his death in 700, some Kaysanites thought he had entered occultation until his reappearance.Daftary, F. (2015). "Shi'i Communities in History". In Daftary, F.; Sajoo, A.B.; Jiwa, S. (eds.). The Shi'i World: Pathways in Tradition and Modernity. I.B. Tauris. pp. 169–209. ISBN 9781784534776. The Twelver theory of occultation crystallized during the first half of the tenth century AD, drawing on both rational and textual arguments. It holds that the life of Muhammad al-Mahdi has been miraculously prolonged and that the Earth cannot be devoid of God's highest proof. In the absence of the Hidden Imam, the leadership vacuum was gradually filled by faqīh jurists. It is popularly held that the Hidden Imam occasionally appears to pious individuals. Accounts of such encounters are numerous and widespread. Every year, millions celebrate Mid-Sha'ban, marking the birth of Muhammad al-Mahdi.

Background Until their deaths, the tenth and eleventh Shia Imams (Ali al-Hadi and Hasan al-Askari, respectively) were held under close surveillance in the garrison town of Samarra by the Abbasids, who are often held responsible in Shia sources for poisoning the two Imams.

Contemporary to the tenth Imam, the Abbasid al-Mutawakkil heavily persecuted the Shia, partly due to a renewed Zaydi opposition. The restrictive policies of al-Mutawakkil towards the tenth Imam were later adopted by his son, al-Mu'tamid, who is reported to have kept the eleventh Imam under house arrest without any visitors. Instead, al-Askari is known to have mainly communicated with his followers through a network of representatives. Among them was Uthman ibn Sa'id, who is said to have disguised himself as a seller of cooking fat to avoid the Abbasid agents, hence his nickname al-Samman. Tabatabai suggests that these restrictions were placed on al-Askari because the caliphate had come to know about traditions among the Shia elite, predicting that the eleventh Imam would father the eschatological Mahdi.

Death of al-Askari Al-Askari died in 260 (873–874) without an obvious heir. Immediately after the death of the eleventh Imam, his main representative, Uthman ibn Sa'id, claimed that the Imam had an infant son, named Muhammad, who was kept hidden from the public out of fear of Abbasid persecution, as they sought to eliminate an expected child of al-Askari, whom persistent rumors described as a savior. Uthman also claimed that he had been appointed to represent Muhammad, who is more commonly known as Muhammad al-Mahdi ().

Being the closest associate of al-Askari, Uthman's assertions were largely accepted by other representatives of al-Askari. Those who accepted the imamate of this Muhammad later formed the Twelvers. The other sects created over the succession of al-Askari disappeared within a hundred years.

Minor Occultation (260-329 AH, 874–941 CE) Thus began a period of about seventy years, later termed the Minor Occultation (), during which it is believed that four successive agents represented Muhammad al-Mahdi, the Hidden Imam. The fourth agent, Abu al-Hasan al-Samarri, is said to have received a letter from Muhammad al-Mahdi shortly before his death in 941 CE. The letter predicted the death of al-Samarri in six days and announced the beginning of the "complete occultation," later called the Major Occultation, which continues to this day. The letter, ascribed to Muhammad al-Mahdi, added that the complete occultation would continue until God permitted him to manifest himself again in a time when the earth would be filled with tyranny.

Upon the death of al-Samarri The Major Occultation, a term coined later, began in 329 (940–941) with the death of the fourth agent, al-Samarri, who did not designate a successor. In this period, which continues today, there is no agent of the Hidden Imam. There is some evidence that the death of the fourth agent also dissolved the underground network of representatives responsible primarily for the collection and distribution of the religious donations. The office of deputyship was thus formally closed. Despite some uncertainty, there were likely early traditions among the Shia that had already predicted the two periods of occultation. These hadiths were previously cited, for instance, by the Waqifites in reference to the two arrests of Musa al-Kazim, the seventh Imam. Nevertheless, the prolonged absence of the Hidden Imam seems to have created widespread doubts among his followers.

Leadership vacuum As both the spiritual and political head of the Twelver community, the occultation of the Hidden Imam left a significant gap. This leadership vacuum was eventually filled by Twelver jurists (), who remain the sole leaders of the Twelver community during the Major Occultation. Often cited to support this transition is a letter received by Ishaq ibn Ya'qub in response to his religious inquiries of the second agent, Abu Ja'far Muhammad ibn Uthman (). The letter, said to have been written by al-Mahdi, stipulated thatA few similar hadiths are attributed to the tenth and eleventh Imams. The traditions also specify that these jurists must be just and knowledgeable in Islamic law. As the absence of the Hidden Imam continued, however, the Twelver jurists evolved from mere transmitters () of hadith to in order to resolve new religious questions that arose over time. Their authority also increased with time to address the need to explicate religious teachings for the community. For instance, as early as the seventh (thirteenth) century, Muhaqqiq al-Hilli () spent the Imam's share of Khums (a type of Islamic alms) on activities that furthered the cause of Shia, as opposed to his predecessors, such as al-Mufid (), who often asked the faithful to save these donations for the rise of al-Mahdi.

Considering that jurists were not directly appointed by the Hidden Imam, it was debated whether their authority should extend to functions with political implications, such as declaring holy war (). It was likely Shahid al-Thani () who first suggested that a (qualified) jurist was the general deputy () of the Hidden Imam whose authority encompassed all prerogatives of the Imam. The transition of Twelver jurists into their new role was facilitated by the formation of Shia states, particularly the Safavid and Qajar dynasties in Iran. For instance, during the Russo-Iranian war of 1804–13, the eminent clerics of Najaf and Isfahan issued a declaration of against the Russians to support the Qajarite Abbas Mirza, who was conducting the campaign. Later on, however, jurists often had to compete with the Shia monarchs for religious authority.

In sum, the politically quiescent approach of the Twelver jurists over time gave way to eventually questioning the legitimacy of Shia monarchs and even attempts to restrict their power through a constitution. This evolution culminated with the concept of () by Khomeini, the religious leader of the Iranian revolution in 1979, who called upon religious scholars to assume an active role after the toppling of Mohammad Reza Pahlavi, the last monarch of Iran.

Doctrinal developments While some traditions, dating back to before 260 (874), might have predicted a second occultation, the sources from the beginning of Major Occultation indicate that the prolonged absence of the Hidden Imam may have led many of the Twelvers to abandon their belief in him. His absence also provided a basis for renewed criticisms at the time, voiced by the Mu'tazilites and Ash'arites. These pressures likely expedited a transition in Twelver arguments from a traditionist to a rationalist approach in order to vindicate the occultation of the Hidden Imam. Abu Sahl al-Nawbakhti (), for instance, argued that the absence of an Imam does not invalidate his religion or law, as with the absence of a prophet. Concerns about inauthentic hadiths, voiced by Tusi () and others, might have given another impetus to this transition.

Starting with Ibn Babawayh () and his student al-Mufid (), Shia scholars began to employ theological arguments modeled on the Mu'tazilite . Of these, the principle of () is an example. At a high level, this principle necessitates that a prophet or an Imam should exist at any time to guide towards God, as the manifestation of His utmost kindness towards His subjects. Other Twelver arguments aim to establish that the Hidden Imam benefits humankind even in occultation, "just as the people benefit from the sun while it is covered by clouds." While the ordinary Twelvers were likely content with the traditions about occultation, the theologist approach to vindicating the Hidden Imam was mainly intended to address the criticisms of the non-Twelver theologians. The two approaches were blended together by Tusi in his substantial monograph Kitab al-Ghayba ().

Twelver doctrine of occultation

The Twelver doctrine of occultation crystallized in the first half of the fourth (tenth) century. In its simplest form, this doctrine states that Muhammad al-Mahdi, the twelfth Imam, did not die but has been concealed by God from humanity. His life has been miraculously prolonged until the day he manifests himself again by God's permission to fill the earth with justice. This occultation continues until the safety of the Imam can be guaranteed, and until humankind is ready to receive his guidance. During the Minor Occultation, which began in 260 (874) with the death of his father and predecessor, the Hidden Imam remained in contact with his followers through the four Babs (gates). During the Major Occultation, which began in 329 (941) and continues to this day, there is no direct communication, though the Hidden Imam still remains responsible in Twelver belief for the inward spiritual guidance of humankind (whereas his outward role begins with his reappearance).

Visitations The Twelvers believe that the primordial light of the prophethood has continued to shine through the ages in the character of the Imams. Thus the Hidden Imam is not viewed as inaccessible in the state of occultation. Indeed, it is popularly held that al-Mahdi occasionally appears to the pious in person or, more commonly, in dreams and visions. The accounts of these encounters are numerous and widespread in the Twelver community. Among these accounts are also the encounters of the prominent religious scholars () with the Hidden Imam.