Abu Ya'qub al-Sijistani
Abu Ya'qub Ishaq ibn Ahmad al-Sijistani () or al-Sijzi () was a 10th-century Persian Ismaili missionary active in the northern and eastern Iranian lands. His life is obscure, but he was a prolific writer, who played a crucial role in the infusion of Neoplatonic ideas into Isma'ili theology. Life Al-Sijistani's life is obscure, as references to him are found mostly in isolation in hostile Sunni heresiological works, while Isma'ili sources usually do not provide any details about him. He was given the nickname 'cottonseed' (Arabic: , Persian: ) in several near-contemporary non-Isma'ili works that mention him, but the origin and significance of it are unknown. What can be gleaned from the sources is that he was a senior missionary () in the Iranian lands of the eastern Islamic world. Nizam al-Mulk reports that a certain Ishaq succeeded Abu Hatim al-Razi as chief at Rayy upon the latter's death on 934, while Ibn al-Nadim mentions a certain Abu Ya'qub as the chief at Rayy in . This Abu Ya'qub was also in charge of the missionary movement () in Upper Mesopotamia and Iraq, with the brothers Abu Muslim and Abu Bakr ibn hammad in Mosul and Ibn Nafis in Baghdad as