Passage 3.14.5
τὸ μὲν δὴ ξόανον τῆς Θέτιδος ἐν ἀπορρήτῳ φυλάσσουσι· Δήμητρα δὲ Χθονίαν Λακεδαιμόνιοι μὲν σέβειν φασὶ παραδόντος σφίσιν Ὀρφέως, δόξῃ δὲ ἐμῇ διὰ τὸ ἱερὸν τὸ ἐν Ἑρμιόνῃ κατέστη καὶ τούτοις Χθονίαν νομίζειν Δήμητρα. ἔστι δὲ καὶ Σαράπιδος νεώτατον τοῦτο Σπαρτιάταις ἱερὸν καὶ Διὸς ἐπίκλησιν Ὀλυμπίου.
The wooden image of Thetis is indeed preserved in secrecy. The Lacedaemonians say that their worship of Demeter Chthonia was handed down to them by Orpheus; yet, in my own opinion, their belief in Demeter as Chthonia arose due to the sanctuary at Hermione. There is also a very recent temple of Sarapis among the Spartans, as well as one dedicated to Zeus under the epithet Olympios.