The Ikhwan Al-Safa (Brethren of Purity) were a group of Sufi
scholars in Basra
who met together sub rosa
As a result of these conversations the Order issued their encyclopaedia of knowledge; the Rasa'il. This mysterious sect espoused beliefs that echoed themes found in Pythagorean and Hermetic doctrines as well as Jabirian and Platonic sources. Their works became quite popular especially among the Ismailis who had their own form of Gnosis. Some, like Henry Corbin, believe the Ikhwan were the voice of the Ismailis themselves. There is also evidence that they influenced the writer of the Picatrix.
They rank high in Esoteric Islam in terms of depth and perception and have influenced many sufic orders and practitioners. They were unusually sympathetic to other religious thinkers for followers of Islam and sought through their investigations to show the similarity between the various types of spiritual development.
Nonetheless there has been heavy debate both in the Middle East and the West concerning this secret brotherhood. Christopher McIntosh has suggested that the Rasa'il may even have inspired the (much later) manifestos of the Rosicrucian Brotherhood. Whether this is indeed a fact matters little in the sense that certainly the synthesis of cosmological and spiritual ideas coupled with science and learning admit to a tradition long upheld by Adepts both of the East and the West.