Al-Hasan ibn Muhammad ibn al-Qasim (Arabic: الحسن بن محمد بن القاسم), known by the sobriquet al-Hajjam (الحجام, lit. 'the barber') was the tenth Idrisid ruler of Morocco, although he held only the capital of Fes and its environs.^[1]

Al-Qasim descended from a cadet branch of the Idrisid dynasty: his grandfather, al-Qasim, was a younger son of the dynasty's second ruler, Idris II.^[2] In 922 or 925 or 928 (medieval and modern sources provide different dates) he rose in revolt against the Fatimid Caliphate's viceroy in Morocco, Musa ibn Abi'l-Afiya, and recovered control of Fes.^[1][3] Two years later, he defeated Ibn Abi'l-Afiya in combat, but was betrayed by Hamid ibn Hamdan, the governor he appointed over Fes, and imprisoned, while Fes was surrendered to Musa.^[1][3]

Ibn Abi'l-Afiya then fell out with Hamid ibn Hamdan and the Fatimids, launching a persecution of the Idrisids, before siding with the Fatimids' enemies, the Umayyad Caliphate of Córdoba in 931.^[3] A complicated struggle followed between the Hamid ibn Hamdun, the Idrisids, their rivals from the Abu Sahl family, Musa ibn Abi'l-Afiya, and the Fatimids under the general Maysur.^[2] Allied with the Fatimids against Ibn Abi'l-Afiya, Hasan's brother al-Qasim Jannun managed to establish an Idrisid emirate in the Rif Mountains in northern Morocco,^[1] before switching his allegiance to the Umayyads in 944.^[2]