Plato, Laws, book 8 42:

καὶ δὴ καὶ μουσικῆσ τὰ μὲν πλεῖστα ὡσαύτωσ διαπεπέρανται, τὰ δὲ ῥαψῳδῶν καὶ τῶν τούτοισ ἑπομένων, καὶ ὅσαι ἐν ἑορταῖσ ἅμιλλαι χορῶν ἀναγκαῖαι γίγνεσθαι, ταχθέντων τοῖσ θεοῖσ τε καὶ τοῖσ μετὰ θεῶν μηνῶν καὶ ἡμερῶν καὶ ἐνιαυτῶν, κοσμηθήσονται τότε, εἴτε τριετηρίδεσ εἴτε αὖ καὶ διὰ πέμπτων ἐτῶν, εἴθ’ ὅπῃ καὶ ὅπωσ ἔννοιαν διδόντων τῶν θεῶν τάξεωσ πέρι διανεμηθῶσιν·