6 You must not adopt the mistaken opinion, that while in dealing with the Gentiles one may appeal to their literature in all other discussions one ought to ignore it; for almost all the books of all these writers— except those who like Epicurus are no scholars— are extremely full of erudition and philosophy. I incline indeed to fancy— the thought comes into my head as I dictate— that you yourself know quite well what has always been the practice of the learned in this matter. I believe that in putting this question to me you are only the mouthpiece of another who by reason of his love for the histories of Sallust might well be called Calpurnius Lanarius. Please beg of him not to envy eaters their teeth because he is toothless himself, and not to make light of the eyes of gazelles because he is himself a mole. Here as you see there is abundant material for discussion, but I have already filled the limits at my disposal.
Source: Letters (New Advent)