I discovered "God's Unruly Friends: Dervish Groups in the Islamic Middle Period 1200-1550" (2006) by Ahmet Karamustafa largely by accident (it was a footnote in another book I had read). The title got me, but it sat on the shelf for a while until I got to it. The book itself is quite short, the text is 102 pages, followed by notes and bibliography. Although (according to the author) little else has been written on the topic, this is a very brief study / introduction. What does the author mean by these deviant dervishes? One lengthy quote:
"Deviant dervishes were thoroughly antinomian in appearance and behavior. They violated all social norms with equal ease and indifference and deliberately embraced a variety of unconventional and socially liminal practices. Perhaps the most potent antinomian feature of new renunciation, certainly the most often cited and criticized, was open disregard for prescribed Islamic ritual practices. The extent to which different groups at different times neglected to fulfill their ritual obligations is impossible to ascertain. Nevertheless, there is little reason to question the accuracy of the reports contained in many sources, hostile and friendly, to the effect that deviant dervishes neither prayed nor fasted. In this context, silence on this issue in sympathetic texts is particularly telling. In Jamal al-Din's sacred biography, for instance, there are only two casual references to ritual prayer, while the hagiography of Otman Baba fares only slightly better in this respect. For its part, the report that Barak Baba's disciples were required to perform prescribed religious practices on pain of forty blows of the bastinado itself reveals the difficulty of enforcing these practices on the dervishes. Moreover, it appears that at least some groups replaced ritual prayer in particular with utterance of simple formulaic expressions. Such was the case with the Qalandars and Abdals of Rum, among whom the utterance of the formula "God is the Greatest" (takbir) clearly had a ritual function and may have come to replace the daily ritual prayer." (p. 17-18)
