Liber de orbe, attributed to Māshā'allāh (d. c.815), a court astrologer of the Abbasid dynasty, was one of the earliest Latin sources of Aristotelian physics. Until recently, its Arabic original could not be identified among Arabic works. Through extensive examination of Arabic manuscripts on exact sciences, I found two manuscripts containing the Arabic text of this Latin work, although neither of them is ascribed to Māshā'allāh: Berlin, Staatsbibliothek zu Berlin, Ms. or. oct. 273, and Philadelphia, Pennsylvania University Library, MS LJS 439. In this paper, I describe these two manuscripts in great detail, so that I confirm their originality of the Liber de orbe, and then by analysing the contents of the Arabic text, I deny the attribution to Māshā'allāh, and identify the title and author as Book on the Configuration of the Orb by Dūnash ibn Tamīm, a disciple of Isaac Israeli (c.855–c.955).