The successor of Musa Kazim (d. 183/799) was his son Ali ar-Rida, who also died in 203/818. He was succeeded by Muhammad at-Taki (d. 220/835) and the latter by Ali al-Naqi (d. 254/868). His son Hasan al-Askari (d. 260/874) had married to a Christian slave-girl, named Narges Khatoon. There however are few controversial accounts for his son, Muhammad Mahdi. J.R.I. Cole writes in "Roots of North Indian Shiism in Iran and Iraq" (New Delhi, 1989, p. 17) that, "Several schism occurred, with some groups saying that Imam Hasan al- Askari had left no heir. Others, especially wealthy Shiis close to the Abbasid court, proclaimed that the Imam had a small son, who supernaturally disappeared and who would one day return to restore the world to justice." Jafar, the brother of Hasan al-Askari is also reported to have been asked about the boy, and he said that he did not know who the boy was. For this reason, Jafar has been vilified by the Shiite sources as Kadhdhab, means "liar." Moojan Momen writes in "An Introduction to Shi'i Islam" (London, 1985, p. 162) that, "Jafar remained unshakable in his assertion that his brother (Hasan al-Askari) had no progeny." Mohammad Manzoor Nomani further writes to this effect that, "As for the truth or correctness of the whole thing, anyone with a little commonsense will conclude that it was a ruse played by a few artful persons to deceive the people" (Ibid. pp. 108-9). Mohammad Manzoor Nomani, the author of "Iranian Revolution" (Karachi, 1988, p. 105) writes that, "Traditions relating to the birth, disappearance and the concealment of the twelfth Imam are given in several chapters of "Usul al-Kafi," such as, from pages 202 to 207, and 333 to 342. A perusal of them will convince that the whole "case" is fabricated and even that has not be done skillfully and well, and the version of Imam Hasan Askari's brother and other family members appears to be correct and worthy of belief."
W.Ivanow however writes in "Brief Survey of the Evolution of Ismailism" (Holland, 1952, p. 6) that, "The fourth Imam (Hasan al-Askari) after Musa Kazim died childless in 260/874, but his relatives, to prevent the sequestration of his property by the state, invented a story of a posthumous male child being born to him. The mysterious baby, however, as they said, became concealed in a cellar in Samarra, a town north of Baghdad, where he is supposed to be still living to come in glory as the promised Mahdi on the judgement day." W.Ivanow concludes his remarks in these words: "If an Imam dies without leaving a son as his successor, it can only mean that not only he personally, but the whole line of his ancestors were not the true Imams. Thus the discontinuation of the line of the Twelvers proved that at least the last several of them were not genuine." (Ibid. p. 9).
At Samarra, is a mosque under which there is a cave (sirdab). The end of one of the chambers of the cave is partitioned off by a gate, and the area behind the gate is called the "chamber of the occultation" (hujrat al-ghayba), and in the corner there is a well, known as the "well of the occultation" (bi'r al-ghayba) down which the twelfth Imam of the Shia Twelvers is supposed to have disappeared.
The following of Jafar Sadik henceforward bifurcated into two branches - the Ismailis, the followers of Ismail, and the Musawite, the supporters of Musa Kazim, who later on came to be known as Twelvers, or Ithna Asharites. J.R.I. Cole writes, "The end of the line of Imams came as a powerful shock to the Twelver community. Early Shii thinkers living after the occultation, or disappearance, of the Imam felt leaderless. In the absence of the infallible Imam, they believed that no one could conduct Friday congregational prayers, lead believers in an aggressive holy war, or collect certain types of land taxes. In short, they felt a profound alienation from the world and generally adopted a quietest political policy." (op. cit., p. 17)
It is further worthwhile to ponder at a focal point that the average Shiite sources concur that Ismail predeceased his father, therefore, Jafar Sadik changed the nass and nominated his another son, Musa Kazim as his successor. Granted that Ismail predeceased his father, then it sharply indicates that Ismail was in reality an Imam for few years or months between the period of his nomination and death. If so, the linage of the Twelvers's Imams should have run as follows:- Jafar Sadik, Ismail, Musa Kazim and so forth. It is curious beyond measure that the Twelvers do not include the name of Ismail between Jafar Sadik and Musa Kazim as per their ruling in the