Plato, Republic, book 3 115:

καὶ τὰ μὲν τοιαῦτα ἀπερεῖν λέγειν, τὰ δ’ ἐναντία τούτων προστάξειν ᾄδειν τε καὶ μυθολογεῖν. ἢ οὐκ οἰεί;