Epictetus, Works, book 4, Πρὸσ τοὺσ περὶ τὸ ἐν ἡσυχίᾳ διάγειν ἐσπουδακότασ. 40:

οὓσ καὶ ὁ Ζεὺσ πεποίηκεν, αὐτὸν δὲ πρὸσ ἑνὶ εἶναι μόνῳ, τῷ ἰδίῳ, τῷ ἀκωλύτῳ, καὶ ἀναγιγνώσκειν ἐπὶ τοῦτο ἀναφέροντα τὴν ἀνάγνωσιν καὶ γράφειν καὶ ἀκούειν.