Encyclopedia of the Brethren of Purity
The Encyclopedia of the Brethren of Purity () also variously known as the Epistles of the Brethren of Sincerity, Epistles of the Brethren of Purity and Epistles of the Brethren of Purity and Loyal Friends is an Islamic encyclopedia in 52 treatises ("rasā'il") written by the mysterious Brethren of Purity of Basra, Iraq sometime in the second half of the 10th century CE (or possibly later, in the 11th century). It had a great influence on later intellectual leading lights of the Muslim world, such as Ibn Arabi, and was transmitted as far abroad within the Muslim world as Al-Andalus. 

The identity and period of the authors of the "Encyclopedia" have not been conclusively established, though the work has been mostly linked with the Isma'ilis. Idris Imad al-Din, a prominent 15th-century Isma'ili missionary in Yemen, credited the authorship of the encyclopedia to Ahmad b. 'Abd Allah b. Muhammad b. Ismail b. Ja'far as-Sadiq, the 9th Isma'ili imam who lived in occultation in the era of Abbasids, at the beginning of the Islamic Golden Age. Some suggest that besides Ismailism, the Brethren of Purity also contains elements of Sufism, Mu'tazilism, Nusairism, Rosicrucianism, etc. Some scholars present the work as Sunni-Sufi.

The subject of the work is vast and ranges from mathematics, music, astronomy, and natural sciences, to ethics, politics, religion, and magic—all compiled for one, basic purpose, that learning is training for the soul and a preparation for its eventual life once freed from the body.
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Encyclopedia of the Brethren of Purity
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