Plato, Laws 907a

εὐφήμει· πῶς γὰρ ἄν; ἀλλʼ οὐ πάντων φυλάκων εἰσὶ μέγιστοι καὶ περὶ τὰ μέγιστα ἡμῖν οἱ πάντες θεοί; πολύ γε. τοὺς δὴ κάλλιστά τε πράγματα φυλάττοντας, διαφέροντάς τε αὐτοὺς φυλακῇ πρὸς ἀρετήν, κυνῶν χείρους καὶ ἀνθρώπων μέσων εἶναι φήσομεν, οἳ τὸ δίκαιον οὐκ ἄν ποτε προδοῖεν ἕνεκα δώρων παρὰ ἀδίκων ἀνδρῶν ἀνοσίως διδομένων;

Are not all gods the greatest of all guardians, and over the greatest things? Yes, by far. Shall we say that those who watch over the fairest things, and who are themselves eminently good at keeping watch, are inferior to dogs and ordinary men, who would never betray justice for the sake of gifts impiously offered by unjust men?