Plato, Meno 93c

φαίης ἄνδρα γεγονέναι; ἔγωγε, πάντων γε μάλιστα. οὐκοῦν καὶ διδάσκαλον ἀγαθόν, εἴπερ τις ἄλλος τῆς αὑτοῦ ἀρετῆς διδάσκαλος ἦν, κἀκεῖνον εἶναι; οἶμαι ἔγωγε, εἴπερ ἐβούλετό γε. ἀλλʼ, οἴει, οὐκ ἂν ἐβουλήθη ἄλλους τέ τινας καλοὺς κἀγαθοὺς γενέσθαι, μάλιστα δέ που τὸν ὑὸν τὸν αὑτοῦ; ἢ οἴει αὐτὸν φθονεῖν αὐτῷ καὶ ἐξεπίτηδες οὐ παραδιδόναι

would you not say that Themistocles was a good man? I would, particularly so. And if any man ever was a teacher of his own virtue, he especially was a good teacher of his? In my opinion, yes, assuming that he wished to be so. But can you suppose he would not have wished that other people should become good, honorable men—above all, I presume, his own son? Or do you think he was jealous of him, and deliberately refused to impart the virtue