Passage 8.44.6
ἐπίκλησις μὲν δή ἐστιν αὐτοῖς Καθαροί, περὶ μεγίστων δὲ αὐτόθι καθεστήκασιν οἱ ὅρκοι· καὶ ὀνόματα μὲν τῶν θεῶν οὐκ ἴσασιν ἢ καὶ εἰδότες οὐ θέλουσιν ἐξαγορεύειν, Καθαροὺς δὲ ἐπὶ τοιῷδε ἄν τις κληθῆναι τεκμαίροιτο, ὅτι αὐτοῖς οὐ κατὰ ταὐτὰ ὁ Πάλλας ἔθυσε καθὰ καὶ ὁ πατήρ οἱ τῷ Λυκαίῳ Διί.
Their epithet, in fact, is "Katharoi" ("Pure Ones"), and among them the most solemn oaths are held sacredly binding. They either do not know the names of the gods, or, if they do know them, refuse to utter them aloud. One might conjecture that they came to be called Katharoi for the following reason: because Pallas did not sacrifice to the Lykaian Zeus in the same manner as his father had.