Admittedly, it is learnt that after leaving Medina, Muhammad bin Ismail made his way towards Iran and Syria accompanied by Maymun al- Qaddah. The bitterest of the Abbasids' enmity was daily growing in intensity. Apprehending lest the enemies should resort to some violent measures against him, Muhammad assumed the name of Maymun al-Qaddah to elude discovery. Thus, the name Maymun al-Qaddah came to be used by two characters at one time. It was also resolved, if the real identity of the Imam be traced, Maymun al-Qaddah was to come forward as Muhammad bin Ismail to sacrifice his own life in order to protect the line of Imamate from extinction.
Henceforward, Muhammad bin Ismail had also a sobriquet of Maymun al-Qaddah to conceal his identity. In fact, Maymun al-Qaddah had a son, named Abdullah (d. 260/874), while Muhammad bin Ismail had also a son at the same time, called Abdullah (d. 212/828), surnamed al-Wafi Ahmad. With the passage of time, Muhammad became known as Maymun al-Qaddah in the places he resided, while Maymun al-Qaddah was treated as Muhammad bin Ismail in the regions he propagated Ismailism. Abdullah, the son of Maymun al-Qaddah was consequently considered as the son of Muhammad bin Ismail in the regions where the Imam had assumed the title of al-Qaddah. It therefore gave rise to the contrivance of a story that Abdullah (al-Wafi Ahmad) was the son of Maymun al-Qaddah on one hand, and Abdullah (bin Maymun al-Qaddah) was the son of Muhammad bin Ismail on other. Later on, it became an instrument for the anti-Fatimid propagandists, notably Ibn Razzam to join the lineage of the Fatimid Imams with that of Abdullah bin Maymun al-Qaddah instead of Abdullah (al-Wafi Ahmad) bin Muhammad bin Ismail. This is known as Qaddahid theory and became a weapon of the later Abbasids to discredit the Fatimid origin in 401/1010.
In the face of these facts, the Ismaili Imams had assumed the titles of the dais in one or more time during the veiled period, which is also sounded expressly in the letter of the Fatimid Imam al-Muizz (341-365/953-975), written in 354/965, addressing to his dai in Sind, called Jaylam bin Shayban. This important letter is well preserved by Idris Imaduddin (d. 872/1468) in the 5th volume of "Uyun'l-Akhbar"(comp. 842/1438). It reads:- ".... These people have arbitrarily limited (the period of Imamate) by (the death of) Muhammad bin Ismail; and when he died, they said about him all what was said by them. They (also) thought that he entrusted the Imamate to some one who was not his son. And that his successor (similarly) entrusted the Imamate (to his own) successors, whose number has (also) reached the number of seven. They thought that the first (of these pseudo-Imams) was Abdullah bin Maymun al-Qaddah. All this is preached in order to prove their theory that there was no Imam after him (i.e., Muhammad bin Ismail), and that those who succeeded him were ordinary people. Thus they have cut what God ordered to be continuing (the line of Imams), opposing the command of God, given in the Koran (47:27). "....and We have made a word to remain after him." The cause of this requires explanation. When the preaching in favour of Muhammad bin Ismail has spread, the Abbasid usurpers tried to lay their hands upon him, i.e. the person whose rights were claimed. Therefore (he and other) Imams went into concealment. Their dais used to refer to them under allegorical names, in accordance with the principle of taqiya, alluding to what they possessed and what was appropriate to them. They used to say, for instance, that the Imam, the son of Muhammad bin Ismail was Abdullah. And this was true. And with regard to his being the son of Maymun al-Qaddah, it was true that he was the son of Maymunu'n naqibat, i.e. of the "Divinely blessed with success in his affairs," of al-Qaddah (the flint) "striking the sparks of guidance", i.e. "lighing the light of the Divine wisdom". Similar allegorical expressions were applied also to other Imams after him, at their own orders and instructions given to their dais. When such allegorical expressions reached those who know nothing about their real implications, and only took them literally, as we mentioned above, they fell into an error, and made others err after them, straying from the straight path. But if they would only do what God has ordered them to do, rallying around the Imams, they surely would know those who were otherwise hidden from them. Just as you know them now. But the blind, who has no one to lead him, or a stick in his hand, falls into an abyss from which no one can save him. The self-conceited fall into sin and error. So beware of thinking that God ever abandons humanity to itself. No, He does not abandon them even for a moment, leaving them without an Imam from the descendants of the Prophet. And the Imams can come to their office only by the commandments relating to Imamate...."
In addition, Hatim bin Imran bin Zuhra (d. 498/1104) writes in his "al-Usul wa'l-Ahkam" that, "The dais used their own names as nick-names for the Imams in order to protect them from persecution; some people were misled by this to such a degree that they said that the Imam, descendant of Muhammad bin Ismail was Abdullah bin Maymun al-Qaddah." According to Arif Tamir in "al-Qaramita" (p. 87), "When Muhammad bin Ismail fled from the east and established in Palmyra in Syria, the centers of his activities; he called himself Maymun al-Qaddah." Syed Abid Ali Abid writes in "Political Theory of the Shiites" (cf. "A History of Muslim Philosophy", ed. by M.M. Sharif, Germany, 1963, 1st. vol., p. 740) that, "As a matter of fact, as the latest research has established beyond any doubt, Maimun was the name adopted by Imam Muhammad when he went into concealment. In other words, during the period of concealment those who were in his confidence knew Imam Muhammad to be a Maimun." Husayn F. al-Hamdani (1901-1962) writes in his "On the Genealogy of Fatimid Caliphs"(Cairo, 1958, p. 18) that, "It is likely that Muhammad b. Ismail, who did not, and could not, according to accounts, live a settled life at one place, went underground during his wanderings by assuming the name of Maymun."
Before biding goodbye to his ancestral abode, Medina, Muhammad had secretly convened an assembly of his dais, inviting them from all the regions. When caliph Harun ar-Rashid came to know the secret assembly, he resolved to arrest Muhammad bin Ismail in Medina. In the meantime, Zubeda, the wife of Harun ar-Rashid and a secret follower of the Imam, managed to send her trusted servant towards the Imam in Medina, informing him the plan of the caliph. Thus, Muhammad bin Ismail had to make his footing out of Medina at once.
Tradition however has it that Muhammad first went to southern Iraq, where he acquired the epithet of al-maktum (veiled one), and then at Nishapur in disguise, where he lodged for some times. Nishapur was one of the most important of the four great cities of Khorasan. The word "Nishapur" is derived from New-Shapur. In Armenian it is called Niu-Shapuh, then became Nishwpur, finally Nishapur. It is situated on the east side of a plain surrounded by hills. To the north and east of the town lies the ridge of Binalud-Kuh, which separates it from the valley of Mashhad and Tus. It was divided into 42 wards, 1 farsakh in length and breath. Muhammad afterwards proceeded towards Ray (the ancient Ragha), a town in Media, about 15 miles from Tehran. Ray was situated in the fertile zone which lies between the mountains and the desert. The Abbasids rebuilt and surrounded it by a ditch. Harun ar-Rashid was also born in Ray and used often to recall with pleasure his native town. In 195/810, caliph Mamun's general Tahir bin Hussain won a victory over caliph Amin's troops near Ray.