Plato, Laws 669c

ἤθη κακὰ φιλοφρονούμενος, χαλεπώτατόν τε αἰσθέσθαι διὰ τὸ τοὺς ποιητὰς φαυλοτέρους εἶναι ποιητὰς αὐτῶν τῶν Μουσῶν. οὐ γὰρ ἂν ἐκεῖναί γε ἐξαμάρτοιέν ποτε τοσοῦτον ὥστε ῥήματα ἀνδρῶν ποιήσασαι τὸ χρῶμα γυναικῶν καὶ μέλος ἀποδοῦναι, καὶ μέλος ἐλευθέρων αὖ καὶ σχήματα συνθεῖσαι ῥυθμοὺς δούλων καὶ ἀνελευθέρων προσαρμόττειν, οὐδʼ αὖ ῥυθμοὺς καὶ σχῆμα ἐλευθέριον ὑποθεῖσαι μέλος ἢ λόγον ἐναντίον ἀποδοῦναι τοῖς ῥυθμοῖς, ἔτι δὲ θηρίων φωνὰς

and, moreover, his blunder is very hard to discern, inasmuch as our poets are inferior as poets to the Muses themselves. For the Muses would never blunder so far as to assign a feminine tune and gesture to verses composed for men, or to fit the rhythms of captives and slaves to gestures framed for free men, or conversely, after constructing the rhythms and gestures of free men, to assign to the rhythms