Fas est et ab hoste doceri.
And this quote in latin means It's right to learn even from an enemy.
Quote in the narrative poem Metamorphoses by Ovid, Roman poet borned in March 20, 43 BC.
Image under Public Domain - scan from "Bibliothek des allgemeinen und praktischen Wissens. Bd. 5" (1905), Abriß der Weltliteratur, Seite 51