Sinan ibn Thabit
, –943, was a medieval scholar who served as the court physician of the Abbasid caliphs al-Muqtadir, al-Qahir, and al-Radi.
As the son of Thabit ibn Qurra and the father of Ibrahim ibn Sinan, Sinan belonged to an illustrious family of astronomers and mathematicians who hailed from the Upper-Mesopotamian city of Harran and who worked at the Abbasid court in Baghdad. He and his family belonged to a religious sect of star worshippers known as the Sabians of Harran, though Sinan was forced to convert to Islam during al-Qahir's brief reign, in which the Abbasid caliph persecuted the Sabians and eventually forced Sinan to flee to Khurasan for a short period. It appears that his children remained Sabian: his sons Ibrahim ibn Sinan and Thabit ibn Sinan both remained Sabian, while one his daughters married into another Sabian family, giving birth to Ibrahim ibn Hilal al-Sabi', who also resisted multiple attempts to convert him from his ancestral faith.
Although Sinan ibn Thabit was primarily known as a physician, having built several hospitals in Baghdad and having overseen a licensing system for physicians, he apparently did not write anything on medicine. His works, which dealt with political philosophy, mathematics, and astronomy, are all lost except for a short treatise on moral philosophy called . His work on political philosophy, which was inspired by Plato's Republic, was criticized by the historian al-Mas'udi.