The word satr (pl. satur) is derived from astar, meaning hide, cover or shield. As it is said, masatra (he concealed enmity), or tastir(to hold within a curtain). According to "Arabic-English Lexicon" (New York, 1872, 4th vol., p. 1304) by Edward William Lane, the word satr means to veil, conceal or hide a thing. The early Ismailis had employed the term satr with regards to those periods in their history when the Imams were hidden from the eyes of their followers. When the animosity of their enemies reached to its extreme, the Ismaili Imams had to hide themeselves to elude discovery. On that juncture, the hujjats represented the Imams in the community. Thus, the hujjat was himself a living proof, acting as the custodian until the time of the Imam's reappearance. This period is called Dawr-i Satr (period of concealment) in Ismaili history. In contrast, the period following the concealment is known as an unveiling (Dawr-i Kashf), or the period of manifestation (Dawr-i Zuhur), when the Imams publicly made their appearance.
With the death of Jafar Sadik in 148/765, Ismail (d. 158/775) and Muhammad (d. 197/813), the gravity of brutal persecutions of the Abbasids had considerably increased. The Abbasids left no chance to grind the Ismailis under the millstone of cruelty. The Ismaili Imams were impelled to thicken their hiding, therefore, the first Dawr-i Satr came into force from 197/813 to 268/882, wherein the Imams were known as al-A'immatu'l masturin i.e., the concealed Imams. Achilles des Souza writes in "Mediation in Islam - an Investigation" (Rome, 1975, p. 35) that, "For the first century and a half after the death of Ismail, the Ismaili Imams remained hidden and little is known. This period could be characterised, as we have seen earlier, as the period of the quietists."
And here we cannot but call attention to a fact that the doctrine of ghayba among the Twelvers should not be confounded with that of the concept of satr among the Ismailis. Seyyed Hossain Nasr writes in this context in his "Ideals and Realities of Islam" (London, 1966, p. 159) that, "The idea of being hidden (mastur) must no, however, be confused with the occultation (ghayba) of the twelfth Imam (of the Twelvers). The first implies simply being hidden from the eyes of the crowd and from public notice, while the second means disappearance from the physical world."
Idris Imaduddin (d. 872/1468) writes in "Zahru'l-ma'ani" (p. 59) that, "He (Wafi Ahmad) was the first of the three concealed Imams by the order of God and His inspiration." Hamiduddin Kirmani (d. 412/1021) also admits in his "ar-Risalat al-Wai'za" (comp. 408/1017) that, "Muhammad bin Ismail became qaim, and after him, the concealed Imams (aima'i masturin) succeeded to the Imamate, who remained hidden on account of the persecution of the tyrants, and these were three Imams, viz., Abdullah, Ahmad and Hussain." Hatim bin Imran bin Zuhra (d. 498/1104) writes in "al-Usul wa'l Ahakam" that, "When Muhammad bin Ismail died, his authority passed to his son, Abdullah bin Muhammad, the hidden one, who was the first to hide himself from his contemporary adversaries." According to Hasan bin Nuh Broachi (d. 939/1533) in "Kitab al-Azhar" (comp. 931/1525) that, "The three hidden Imams were Abdullah bin Muhammad, Ahmad bin Abdullah, surnamed at-Taqi and Hussain bin Ahmad." The fact that the Dawr-i Satr virtually came into force in the time of Wafi Ahmad has been also asserted by the modern scholars, such as W.Ivanow, Dr. Sami Nassib Makarem, Sir Johj Glubb, Husayn F. al-Hamdani, etc.
Shahrastani (1076-1153) writes in "Kitab al-milal wa'l nihal" (p. 164) that, "Then begins the era of the hidden Imams, who went about secretly but sent out emissaries, who appeared openly on their behalf. They hold that the world can never be without an Imam who is alive and a qaim, either visible and manifest, or hidden and concealed. When the Imam is manifest it is possible for his hujjat (proof) to be hidden, but if the Imam is hidden it is necessary for his hujjat and emissaries to be manifest."
On account of the strictness of Imam's concealment, when his hujjats were accepting on his behalf the oath of allegiance from neophytes, they used to tell them that they should obey the Lord of the Time (Sahib al-Asr or Waliyul Asr) without pronouncing the name of the Imam. This practice was in use among the neophytes through the whole period of the concealment of the Imams.
Summing up the condition of the hidden Imams in the veiled period, Ibn Khaldun writes in his "Muqaddimah" (1st vol., pp. 44-5) that, "These people (Imams) were constantly on the move because of the suspicions various governments had concerning them. They were kept under observation by the tyrants, because their partisans were numerous and their propaganda had spread far and wide. Time after time they had to leave the places where they had settled. Their men, therefore, took refuge in hiding, and their (identity) was hardly known, as the poet says: `If you would ask the days what my name is, they would not know, and where I am, they would not know where I am.'"
Wafi Ahmad settled in Nihawand, and betrothed to Amina, daughter of Hamdan, son of Mansur bin Jowshan, who was from Kazirun. By this wife, the Imam had a son, Ali bin Abdullah, surnamed al-Layth, and a daughter, Fatima. The brother of Wafi Ahmad also married here and had a posterity.
Meanwhile, the Abbasids intensified their operations, thus Wafi Ahmad made his son as the chief of the Ismaili mission, and himself went from the knowledge of the people, so that none of his followers and other knew where he was. It is however known from the fragment of the traditions that he had gone to Syria and lived in the castle of Masiyaf for some time.