Plato, Republic, book 7 355:

ἀλλὰ δή, εἶπον, μὴ δυνατοὶ οἵτινεσ δοῦναί τε καὶ ἀποδέξασθαι λόγον εἴσεσθαί ποτέ τι ὧν φαμεν δεῖν εἰδέναι;