Zandaqa

[3] It originally referred to the adherents of Manichaeism,[3] but then came to be applied to those who were accused of having heretical beliefs and actions deemed as threatening by Islamic authorities.

[5] By the time of the eighth-century Abbasid Caliphate however, the meaning of the word zindīq and the adjectival zandaqa had broadened and could loosely denote many things: Gnostic Dualists as well as followers of Manichaeism, agnostics, and atheists.

[7][8] A history of the time states cites the first Abbasid caliph Abu al-'Abbas As-Saffah as having said "tolerance is laudable, except in matters dangerous to religious belief, or to the sovereign's dignity.

Many of these converts had previously been Manichaeans, and Manichaeaism with its well developed missionary ideals had undergone a slight resurgence during early caliphate rule.

The threat was perceived to be especially evident in the quasi-scientific manner in which the Manichaeans posed unsettling questions, their skill at creating a favourable impression in public debate, and their ability in defending their own intellectually-appealing world-view.