This paper presents a unique manuscript copy of a fifth/eleventh-century Maghribī commentary on al-Bāqillānī’s Kitāb al-Tamhīd. The work, entitled al-Tasdīd fī sharḥ al-Tamhīd, was written by ‘Abd al-Jalīl b. Abī Bakr al-Dībājī —also known as Ibn al-Ṣābūnī— who had studied the Kitāb al-Tamhīd with al-Bāqillānī’s disciples in Qayrawān. The present study first reviews the transmission of al-Bāqillānī’s work to the Islamic west. It then continues to present the author of the commentary, to reconstruct the work’s genesis and to describe its (...) content. The final section focuses on a sample chapter and argues that al-Dībājī follows al-Bāqillānī’s later position on a specific theory —the so-called theory ofaḥwāl— of which the Tamhīd strongly disapproved. The Tasdīd is one of the oldest texts of Maghribī Ash‘arism that has come down to us and provides valuable new insights into the school’s early history in the Islamic west. (shrink)