Abu’l-Qāsim ʿAbdallāh ibn Ali (Arabic: أبو القاسم عبد الله بن علي; 905 – September/October 949), better known by his regnal name al-Mustakfī bi’llāh (Arabic: المستكفي بالله, lit. 'Desirous of Being Satisfied with God Alone') was the Abbasid caliph in Baghdad from 944 to 946.

Al-Mustakfi was a younger son of Caliph al-Muktafi, and hence a rival to the line of Caliph al-Muqtadir that reigned in 908–944, a period during which the Abbasid Caliphate nearly collapsed, and caliphs became puppets at the hands of rival warlords. Al-Mustakfi himself was installed on the throne by Tuzun, a Turkish general who deposed and blinded the previous caliph, al-Muttaqi. In the power vacuum left after Tuzun's death in August 945, al-Mustakfi tried to regain some of his freedom of action, initiating anti-Shi'a measures, but the same vacuum allowed the Buyids to capture Baghdad. Al-Mustakfi was forced to recognize the Buyids as legitimate rulers and awarded them regnal titles, but was soon accused of plotting against them and deposed in January (or March) 946. He spent the final years of his life in prison. His son attempted to claim the caliphate in c. 968, but failed.