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.