Saʿd al-Dīn Muḥammad ibn al-Muʾayyad ibn Ḥamuwayh al-Ḥamuwayī al-Juwaynī (1190/99 – 1252/60) was a Persian Ṣūfī shaykh from a prominent Ṣūfī family. He belonged to the order of the Kubrāwiyya. A prolific writer, he is credited with at least 47 works plus poetry. He was a noted mystic and much of his writing is esoteric and numerological. Born and died in Khorasan, he studied in Damascus, went on a pilgrimage to Mecca and lived for a time in Tabrīz and Mosul. He fled the Mongol invasion of Khwārazm in 1220. By 1242 he had contracted an illness that resulted in the loss of a finger.