Macrobius, Saturnalia 6.2
“I fear that, in my eagerness to show how much Vergil accomplished from his reading of the ancients, and what blossoms and what ornaments he poured forth from all of them into his own poetry, I may accidentally offer an opportunity of for criticism to those uncultured and malignant fools who censure such a man for his usurpation of other’s works, not considering that this is the fruit of reading: to imitate those things which you approve in others, and to turn the sayings of others which you marvel at into your own use by a fitting turn. Our poets have done this among themselves, just as much as the best of the Greeks did. And, to avoid talk of foreign precedent, I could show with numerous examples how much the authors of our ancient canon have lifted from one another.”
Etsi vereor me, dum ostendere cupio quantum Virgilius noster ex antiquiorum lectione profecerit et quos ex omnibus flores vel quae in carminis sui decorem ex diversis ornamenta libaverit, occasionem reprehendendi vel inperitis vel malignis ministrem, exprobrantibus tanto viro alieni usurpationem, nec considerantibus hunc esse fructum legendi, aemulari ea quae in aliis probes et quae maxime inter aliorum dicta mireris in aliquem usum tuum oportuna derivatione convertere, quod et nostri tam inter se quam a Graecis et Graecorum excellentes inter se saepe fecerunt. Et, ut de alienigenis taceam, possem pluribus edocere quantum se mutuo conpilarint bibliothecae veteris auctores.