Al-Nu'man's most prominent work, the Da'a'im al-Islam ( "The Pillars of Islam"), which took nearly thirty years to complete, is an exposition of Isma'ili jurisprudence. This work was finally completed during the reign of the fourth caliph, al-Mu'izz li-Din Allah (r. 953-975 CE/ 341-365 AH), was accepted in its time as the official code of the Fatimid Caliphate, and serves to this day as the primary source of religious law (sharia) for some Musta'li communities, particularly Tayyibi Isma'ilis.
Al-Nu'man's most prominent work, Da'a'im al-Islam ("The Pillars of Islam"), which took nearly thirty years to complete, is an exposition on Isma'ili jurisprudence. This work was completed during the reign of the fourth caliph, al-Mu'izz li-Din Allah (r. 953-975 CE/ 341-365 AH), and has been accepted as the official code for the Fatimid Caliphate. It continues to serve as a primary source of religious law (sharia) for some Musta'li communities, particularly Tayyibi Isma'ilis.