Epictetus, Works, book 4, Περὶ ἐλευθερίας.? 140:

οὐ ψυχρὸν καὶ ταλαίπωρον ὑποληψείδιον ἐκ λόγων εἰκαίων ὡς ἐκ τριχὸς ἠρτημένον, ἀλλὰ ἰσχυρὸν καὶ χρηστικὸν καὶ ὑπὸ τοῦ διὰ τῶν ἔργων γεγυμνάσθαι μεμυημένον.