Plato, Laws 777d

μέλλοντας ῥᾷον δουλεύσειν, ἀσυμφώνους τε εἰς δύναμιν ὅτι μάλιστα, τρέφειν δʼ αὐτοὺς ὀρθῶς, μὴ μόνον ἐκείνων ἕνεκα, πλέον δὲ αὑτῶν προτιμῶντας· ἡ δὲ τροφὴ τῶν τοιούτων μήτε τινὰ ὕβριν ὑβρίζειν εἰς τοὺς οἰκέτας, ἧττον δέ, εἰ δυνατόν, ἀδικεῖν ἢ τοὺς ἐξ ἴσου. διάδηλος γὰρ ὁ φύσει καὶ μὴ πλαστῶς σέβων τὴν δίκην, μισῶν δὲ ὄντως τὸ ἄδικον, ἐν τούτοις τῶν ἀνθρώπων ἐν οἷς αὐτῷ ῥᾴδιον ἀδικεῖν· ὁ περὶ τὰ τῶν δούλων οὖν ἤθη καὶ πράξεις γιγνόμενός τις ἀμίαντος

not to allow the slaves, if they are to tolerate slavery quietly, to be all of the same nation, but, so far as possible, to have them of different races,—and the other is to accord them proper treatment, and that not only for their sakes, but still more for the sake of ourselves. Proper treatment of servants consists in using no violence towards them, and in hurting them even less, if possible, than our own equals. For it is his way of dealing with men whom it is easy for him to wrong that shows most clearly whether a man is genuine or hypocritical in his reverence for justice and hatred of injustice. He, therefore, that in dealing with slaves proves himself, in his character and action,