Passage 5.27.5
καὶ ἄλλο ἐν Λυδίᾳ θεασάμενος οἶδα διάφορον μὲν θαῦμα ἢ κατὰ τὸν ἵππον τὸν Φόρμιδος, μάγων μέντοι σοφίας οὐδὲ αὐτὸ ἀπηλλαγμένον. ἔστι γὰρ Λυδοῖς ἐπίκλησιν Περσικοῖς ἱερὰ ἔν τε Ἱεροκαισαρείᾳ καλουμένῃ πόλει καὶ ἐν Ὑπαίποις, ἐν ἑκατέρῳ δὲ τῶν ἱερῶν οἴκημά τε καὶ ἐν τῷ οἰκήματί ἐστιν ἐπὶ βωμοῦ τέφρα· χρόα δὲ οὐ κατὰ τέφραν ἐστὶν αὐτῇ τὴν ἄλλην.
I have also personally seen something else in Lydia, different indeed in wonder from the horse of Phormis, yet likewise not free from the skill of magicians. For the Lydians called "Persians" have sanctuaries in a city named Hierocaesareia and in Hypaepa; and in each of these temples there is a chamber, and in the chamber on an altar there is ash. This ash, however, in its entire appearance is not like ordinary ash.