Epictetus, Works, book 4, Πρὸσ τοὺσ μαχίμουσ καὶ θηριώδεισ. 19:

" τί οὖν ἔλεγεσ, ὅτι ἄνθρωπόσ ἐστιν; μὴ γὰρ ἐκ ψιλῆσ μορφῆσ κρίνεται τῶν ὄντων ἕκαστον; ἐπεὶ οὕτωσ λέγε καὶ τὸ κήρινον μῆλον εἶναι.