Abū'l-Ḥusayn Hilāl b. Muḥassin b. Ibrahīm al-Ṣābi' (born : 358 A.H/969 A.D, died :447-448 A.H/1056 A.D) (aged 90 lunar) ابو حسين هلال بن محسن بن ابراهيم الصابئ) was a historian, bureaucrat, and writer of Arabic. Born into a family of Sabian bureaucrats, al-Ṣābi converted to Islam in 402-403 A.H/1012 AD. First working under the Buyid amir Ṣamṣām al-Dawla, he later became the Director of the Chancery under Baha' al-Daula's vizier Fakhr al-Mulk.
Hilal al-Sabi' is the author of numerous books, not all of which have survived. Bureaucratic matters and matters of the court were his main themes, along with history.
Perhaps his most famous book is the Rusum dar al-khilafa which is a manual for behavior and work in the Abbasid court of late Buyid Baghdad. Though it is designed as a set of instructions and advice, the book contains numerous statistics, anecdotes and historical asides.
Only of the beginning of this work has survived, which deals with the viziers of the caliph Al-Muqtadir.
This too survives only in fragmentary form, but its fragments fill a gap in the chronicles of the late Buyid era, up to the year 393 hijri (1003 AD).