Epictetus, Works, book 4, Περὶ ἀφοβίασ. 8:

πρὸσ τούτοισ δὲ φύσει γενναῖον καὶ μεγαλόψυχον καὶ ἐλεύθερον γενόμενον ὁρᾷ, διότι τῶν περὶ αὐτὸ τὰ μὲν ἀκώλυτα ἔχει καὶ ἐπ’ αὐτῷ, τὰ δὲ κωλυτὰ καὶ ἐπ’ ἄλλοισ· ἀκώλυτα μὲν τὰ προαιρετικά, κωλυτὰ δὲ τὰ ἀπροαίρετα.