Passage 4.29.6
ἐς δὲ τὸ συνέδριον οἱ Μεσσήνιοι τὸ Ἀχαιῶν ἐπὶ τῷδε οὔ μοι δοκοῦσιν ἐσελθεῖν κατʼ ἀρχάς. Λακεδαιμονίοις αὐτεπάγγελτοι βοηθήσοντες ἀφίκοντο ὑπὸ Πύρρου τοῦ Αἰακίδου πολεμουμένοις, καί σφισιν ἀπὸ τῆς εὐεργεσίας ταύτης ἤδη τὰ ἐκ τῆς Σπάρτης εἰρηνικώτερα ὑπῆρχεν. οὔκουν ἀνακινῆσαι τὸ ἔχθος ἐβούλοντο ἐς τὸ συνέδριον συγχωρήσαντες, οἳ Λακεδαιμονίων μάλιστα πολέμιοι ἐκ τοῦ φανεροῦ καθεστήκεσαν.
It is my opinion that the Messenians did not at first join the council of the Achaeans for the following reason. They voluntarily aided the Lacedaemonians when the latter were at war with Pyrrhus, the son of Aeacides; and as a result of this service, relations with Sparta thereafter became somewhat more peaceful. Thus the Messenians, openly the bitterest enemies of Sparta, did not wish to revive their hostility by joining the Achaean council.