Most of the adherents of Ismaili faith during the period under review are hardly known due to the practice of taqiya. But, the Ismaili dais had best records of it, who became the source of informations for the later Ismaili authorities. Among the secret followers, the name of Zubaida, the wife of caliph Harun ar-Rashid is a significant. She was the daughter of the Abbasid caliph Mansur's elder son, Jafar; and her mother was Salsal, the sister of Harun ar-Rashid's own mother, named Khaizuran. Zubaida was thus the cousin of Harun ar-Rashid, and professed batini tariqah of the Ismailis secretly. Her marriage with Harun ar-Rashid took place in 164/781. Zubaida, in middle life, built herself a palace of her own, surrounded by a very large garden. She had employed a large staff of secretaries and agents to manage the properties she had acquired in all over the empire. She also undertook projects for the digging of canals for irrigation and water supply. She was famous for the extensive engineering works which she had carried out in Mecca, to bring water sufficient for the increasing number of pilgrims. One of the most of her projects was the improvement of the pilgrim road across 900 miles of desert from Kufa to Medina and Mecca, which still in south Kufa is known as Darb Zubaida. She died in 226/841, about 32 years after her husband's death. It appears that she advocated Ismaili faith before her marriage in 164/781 and used to inform Imam Muhammad bin Ismail in advance the measures of Harun ar-Rashid through her trusted agents. It also appears that her close link with the Imam had ceased after the death of Muhammad bin Ismail.
According to "Zahru'l-ma'ani", "Muhammad spread religious knowledge, explained esoteric doctrines, and revealed to the chosen ones the great mystery, so much of these as never was revealed by any Imam before him."
Some sources state that after the massacre of Abul Khattab and his followers in Kufa, the remnants joined al-Mubarakiyya, and that out of this union arose a group who preached that Muhammad bin Ismail was the last Imam, anticipating his return. It was however this group who was the predecessors of the later Qarmatians, who refused to accept the death of Muhammad bin Ismail, who, according to them remained alive and would return in the imminent future as the promised Mahdi or Qaim. The main loyalist branch of Ismailism however traced the Imamate in the progeny of Muhammad bin Ismail.
The period of Muhammad bin Ismail also saw an early growth of the Sufism in Islam. The eminent Sufis who flourished in the period under review were Hasan Basri (d. 110/728), Ibrahim bin Adham (d. 160/776), Abu Hashim Kufi (d. 160/775-6), Rabia Basri (d. 185/801), Shaqiq Balkhi (d. 194/810), etc.