This paper introduces a dual-text manuscript produced in 833/1430 at Herat in the library of the Timurid prince, Bāysunghur (1399-1437), which has escaped previous scholarly attention. Its scribe, Sa‘d al-Mashhadī, was previously known only for his copy of the Tārīkh-i Jahāngushā of ‘Atā-Malik Juvaynī, as well as reports on his works in the Arża-dāsht by Bāysunghur’s chief librarian, Ja‘far Tabrīzī, where he is referred to as Maulānā Sa‘d al-Dīn. However, there is no other information about Sa‘d as a calligrapher or an artist in contemporary or later sources. After a brief description of the manuscript, which bears the name of Bāysunghur on its binding, the article attempts to discover a fuller picture of Sa‘d al-Mashhadī’s identity. A number of biographical dictionaries appear to equate him with a poet called Ḥāfiẓ Sa‘d, an exact contemporary who was also a prominent riddle writer, evidently attached to the court of Bāysunghur. This investigation in turn provides further evidence of an intellectual exchange between the courts of Bāysunghur Mīrzā and Ibrāhīm-Sultan, where the celebrated writer ‘Alī Yazdī also composed riddles, including some concerning Sa‘d al-Dīn.