Passage 4.32.4
παραγενέσθαι δὲ Ἀριστομένην καὶ τῷ περὶ Λεῦκτρα ἀγῶνι ἐθέλουσιν οὐ μετὰ ἀνθρώπων ἔτι ὄντα, καὶ ἀμῦναί τε αὐτόν φασι Θηβαίοις καὶ μάλιστα γενέσθαι τοῦ ἀτυχήματος Λακεδαιμονίοις αἴτιον. ἐγὼ δὲ Χαλδαίους καὶ Ἰνδῶν τοὺς μάγους πρώτους οἶδα εἰπόντας ὡς ἀθάνατός ἐστιν ἀνθρώπου ψυχή, καί σφισι καὶ Ἑλλήνων ἄλλοι τε ἐπείσθησαν καὶ οὐχ ἥκιστα Πλάτων ὁ Ἀρίστωνος· εἰ δὲ ἀποδέχεσθαι καὶ οἱ πάντες ἐθελήσουσιν, ἐκεῖνό γε ἀντειπεῖν οὐκ ἔνεστι μὴ οὐ τὸν πάντα αἰῶνα Ἀριστομένει τὸ μῖσος τὸ ἐς Λακεδαιμονίους ἐνεστάχθαι.
They say also that Aristomenes was present willingly at the battle of Leuctra, though no longer among the living, and the Thebans claim he aided them and was chiefly responsible for the disaster that befell the Lacedaemonians. Now I know that the Chaldeans and the Magi of India were the first to declare the human soul immortal, and certain Greeks adopted this belief from their teachings, most notably Plato, the son of Ariston. If all men should accept this doctrine, it would then be impossible to deny that Aristomenes' hatred for Sparta persisted eternally.