Occultation of Imam al-Mahdi (a)
The Occultation of Imam al-Mahdi refers to the belief that the last and twelfth Shi'a Imam, Imam al-Mahdi (a), was disappeared. The occultation was conducted at the permission and will of God and is one of the basic and mandatory teachings of the Twelver Shi'a sect. In Hadiths that have discussed the motives behind occultation, the idea of putting the Shi'a to test has been cited.
According to Shi'a teachings, Imam al-Mahdi (a) has had two occultations: The Minor Occultation, which lasted sixty nine lunar years, and the Major Occultation, which continues to the present day. During the Minor Occultation, Imam al-Mahdi (a) communicated with the Shi'a through the four deputies, but during the Major Occultation this communication does not exist and the Shi'a must refer to the scholars for their religious needs.
In order to explain occultation, Shi'a researchers have written numerous books on the issue, the most famous of which are al-Nu'mani's book on occultation (Al-Ghayba) and al-Shaykh al-Tusi's Book on occultation (Kitab al-Ghayba).
Defining the Topic
According to Shi'a belief, God never leaves the earth without His deputy, the ultimatum, and infallible Imam. After the martyrdom of the eleventh Imam (a) in 260/864, the twelfth Imam, Muhammad b. al-Hasan al-'Askari (a), who was born in 255/646, inherited the position. By God's knowledge and will, the twelfth Imam disappeared from sight in 260/874, although he is still alive and shall reappear one day to free the world from the violence and injustice that fills it, in order to place justice and fairness instead.
The word ghayba (غَيْبَة, occultation) is derived from the root "gh-y-b" (غ ی ب). Its definition is opposite to presence and is used to convey disappearance from sight and camouflage.