Epictetus, Works, book 4, Περὶ ἐλευθερίασ. 120:

‐ Καὶ τίσ ἡ ζημία τῷ δήσαντι τὸν αὑτοῦ δοῦλον, ἣν δοκεῖσ; ‐ Τὸ δῆσαι· τοῦτο ὃ καὶ σὺ ὁμολογήσεισ, ἂν θέλῃσ σῴζειν, ὅτι ἄνθρωποσ οὐκ ἔστι θηρίον, ἀλλ’ ἥμερον ζῷον.