إخوان الصفا
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.