Plato, Laws 711b

καὶ μὴν τοῦτό γʼ ἂν ἴδοις ἐν αὐτῇ τὸ νυνδὴ λεγόμενον. τὸ ποῖον; οὐδὲν δεῖ πόνων οὐδέ τινος παμπόλλου χρόνου τῷ τυράννῳ μεταβαλεῖν βουληθέντι πόλεως ἤθη, πορεύεσθαι δὲ αὐτὸν δεῖ πρῶτον ταύτῃ, ὅπῃπερ ἂν ἐθελήσῃ, ἐάντε πρὸς ἀρετῆς ἐπιτηδεύματα, προτρέπεσθαι τοὺς πολίτας, ἐάντε ἐπὶ τοὐναντίον, αὐτὸν πρῶτον πάντα ὑπογράφοντα τῷ πράττειν,

You would, however, see in it an illustration of what we spoke of just now. What was that? The fact that a monarch, when he decides to change the moral habits of a State, needs no great efforts nor a vast length of time, but what he does need is to lead the way himself first along the desired path, whether it be to urge the citizens towards virtue’s practices or the contrary; by his personal example he should first trace out the right lines, giving praise and honor to these things,