Plato, Meno 89b

καὶ γὰρ ἄν που καὶ τόδʼ ἦν· εἰ φύσει οἱ ἀγαθοὶ ἐγίγνοντο, ἦσάν που ἂν ἡμῖν οἳ ἐγίγνωσκον τῶν νέων τοὺς ἀγαθοὺς τὰς φύσεις, οὓς ἡμεῖς ἂν παραλαβόντες ἐκείνων ἀποφηνάντων ἐφυλάττομεν ἂν ἐν ἀκροπόλει, κατασημηνάμενοι πολὺ μᾶλλον ἢ τὸ χρυσίον, ἵνα μηδεὶς αὐτοὺς διέφθειρεν, ἀλλʼ ἐπειδὴ ἀφίκοιντο εἰς τὴν ἡλικίαν, χρήσιμοι γίγνοιντο ταῖς πόλεσι. εἰκός γέ τοι, ὦ Σώκρατες. ἆρʼ οὖν ἐπειδὴ οὐ φύσει οἱ ἀγαθοὶ ἀγαθοὶ γίγνονται,

No, for then, I presume, we should have had this result: if good men were so by nature, we surely should have had men able to discern who of the young were good by nature, and on their pointing them out we should have taken them over and kept them safe in the citadel, having set our mark on them far rather than on our gold treasure, in order that none might have tampered with them, and that when they came to be of age, they might be useful to their country. Yes, most likely, Socrates. So since it is not by nature that the good become good,