Plato, Meno 88c

σφόδρα. οὐκοῦν συλλήβδην πάντα τὰ τῆς ψυχῆς ἐπιχειρήματα καὶ καρτερήματα ἡγουμένης μὲν φρονήσεως εἰς εὐδαιμονίαν τελευτᾷ, ἀφροσύνης δʼ εἰς τοὐναντίον; ἔοικεν. εἰ ἄρα ἀρετὴ τῶν ἐν τῇ ψυχῇ τί ἐστιν καὶ ἀναγκαῖον αὐτῷ ὠφελίμῳ εἶναι, φρόνησιν αὐτὸ δεῖ εἶναι, ἐπειδήπερ πάντα τὰ κατὰ τὴν ψυχὴν αὐτὰ μὲν καθʼ αὑτὰ οὔτε ὠφέλιμα οὔτε βλαβερά ἐστιν, προσγενομένης δὲ φρονήσεως

Most certainly. And in brief, all the undertakings and endurances of the soul, when guided by wisdom, end in happiness, but when folly guides, in the opposite? So it seems. Then if virtue is something that is in the soul, and must needs be profitable, it ought to be wisdom, seeing that all the properties of the soul are in themselves neither profitable nor harmful, but are made either one or the other