Dio Chrysostom, Orationes

συγγίγνεσθαί τε μετὰ ταῦτα οὐχ ἅπασιν, ἀλλὰ τοῖς ἄριστα πρὸς ἀλήθειαν πεφυκόσι καὶ τοῦ θεοῦ ξυνιέναι δυναμένοις, οὓς Πέρσαι μάγους ἐκάλεσαν, ἐπισταμένους θεραπεύειν τὸ δαιμόνιον, οὐχ ὡς Ἕλληνες ἀγνοίᾳ τοῦ ὀνόματος οὕτως ὀνομάζουσιν ἀνθρώπους γόητας. ἐκεῖνοι δὲ τά τε ἄλλα δρῶσι κατὰ λόγους ἱεροὺς καὶ δὴ τῷ Διὶ τρέφουσιν ἅρμα Νισαίων ἵππων· οἱ δέ εἰσι κάλλιστοι καὶ μέγιστοι τῶν κατὰ τὴν Ἀσίαν· τῷ δέ γε Ἡλίῳ ἕνα ἵππον.

and that afterwards he kept company not with everyone, but with those best suited by nature to truth and able to understand the god, whom the Persians called Magi — men who knew how to serve the divine power, not as the Greeks, in ignorance of the name, use this name for wizards. These men do all other things according to sacred teachings, and in particular they keep for Zeus a chariot of Nisaean horses — these are the finest and largest in Asia — and for the Sun a single horse.