Plato, Laws 759d

τούτοις χρῆσθαι. κατʼ ἐνιαυτὸν δὲ εἶναι καὶ μὴ μακρότερον τὴν ἱερωσύνην ἑκάστην, ἔτη δὲ μὴ ἔλαττον ἑξήκοντα ἡμῖν εἴη γεγονὼς ὁ μέλλων καθʼ ἱεροὺς νόμους περὶ τὰ θεῖα ἱκανῶς ἁγιστεύσειν· ταὐτὰ δὲ καὶ περὶ τῶν ἱερειῶν ἔστω τὰ νόμιμα. τοὺς δὲ ἐξηγητὰς τρὶς φερέτωσαν μὲν αἱ τέτταρες φυλαὶ τέτταρας, ἕκαστον ἐξ αὑτῶν, τρεῖς δέ, οἷς ἂν πλείστη γένηται ψῆφος, δοκιμάσαντας, ἐννέα πέμπειν εἰς Δελφοὺς ἀνελεῖν ἐξ ἑκάστης τριάδος ἕνα· τὴν δὲ δοκιμασίαν αὐτῶν

Each priestly office should last for one year and no longer; and the person who is to officiate in sacred matters efficiently according to the laws of religion should be not less than sixty years old: and the same rules shall hold good also for priestesses. For the interpreters the tribes shall vote four at a time, by three votings, for four men, one from each tribe; and when the three men for whom most votes are cast have been tested, they shall send the other nine to Delphi for the oracle to select one from each triad;