Sextus Empiricus, Against the Professors of Liberal Arts 1.203 = (in part) Orph. 882.I Bernabé

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τὸ δὲ ὅμοιον καὶ ἀνόμοιον ἐκ τῆς δεδοκιμασμένης λαμβάνεται συνηθείας, δεδοκιμασμένη δὲ καὶ ἀρχαιοτάτη ἐστὶν ἡ Ὁμήρου ποίησις· ποίημα γὰρ οὐδὲν πρεσβύτερον ἧκεν εἰς ἡμᾶς τῆς ἐκείνου ποιήσεως. διαλεξόμεθα ἄρα τῆι Ὁμήρου κατακολουθοῦντες συνηθείαι. ἀλλὰ πρῶτον μὲν οὐχ ὑπὸ πάντων ὁμολογεῖται ποιητὴς ἀρχαιότατος εἶναι Ὅμηρος· ἔνιοι γὰρ Ἡσίοδον προήκειν τοῖς χρόνοις λέγουσιν, Λίνον τε καὶ Ὀρφέα καὶ Μουσαῖον καὶ ἄλλους παμπληθεῖς.

But the similar and the dissimilar are grasped from accepted usage, and respected and most ancient is the poetry of Homer. For no poem older than his poetry has come down to us. In our speech, then, we will follow the customary usage of Homer. But, first of all, Homer is not universally agreed to be the oldest poet; for some say that Hesiod preceded him in time, and Linus and Orpheus and Musaeus and a whole lot of others.

Relevant guides Orpheus