What is "al-mada'ini"

Abū'l-Ḥasan ʿAli ibn Muḥammad ibn ʿAbd Allāh ibn Abī Sayf (752–843), better known by his nisba of al-Madāʾinī ("from al-Mada'in"), was an early Arab scholar, active under the Abbasids in Iraq in the first half of the 9th century. A scholar of many interests, he wrote over 200 works, but is best known as a historian.