Quapropter bono christiano, sive mathematici, sive quilibet impie divinantium, maxime dicentes vera, cavendi sunt, ne consortio daemoniorum animam deceptam, pacto quodam societatis irretiant.
II, xvii, 37
Translation published in Mathematics in Western Culture (1953): The good Christian should beware the mathematician and all those who make empty prophecies. The danger already exists that the mathematicians have made a covenant with the devil to darken the spirit and to confine man in the bonds of hell.
Modern translation by J.H. Taylor in Ancient Christian Writers (1982): Hence, a devout Christian must avoid astrologers and all impious soothsayers, especially when they tell the truth, for fear of leading his soul into error by consorting with demons and entangling himself with the bonds of such association.
Note: The well known, but incorrect English translation was published on page 3 of Morris Kline's Mathematics in Western Culture (1953). This book is a favorite with math students and is still in print. The Latin word mathematici derives from the Greek meaning of "something learned" and refers mainly to astrologers. This was the chief branch of mathematics at the time but has been replaced in modern times by a plethora of other branches. According to the Shorter Oxford English Dictionary, 3rd edition, the word "mathematician" still meant astrologer as late as 1710.