ἐπὶ ξυροῦ ἵσταται ἀκμῆς

From LSJ

Ἤθη πονηρὰ τὴν φύσιν διαστρέφει → Bonae indolis venena sunt mores mali → Verdorbne Sitten sind verderblich der Natur

Menander, Monostichoi, 203