Passage 4.26.1
τὸ δὲ ἀπὸ τούτου τόν τε ἄλλον χρόνον ἐνέκειτό σφισι τὸ ἐς Λακεδαιμονίους μῖσος καὶ τὴν ἔχθραν ἐς αὐτοὺς μάλιστα ἐπεδείξαντο ἐπὶ τοῦ γενομένου Πελοποννησίοις πρὸς Ἀθηναίους πολέμου· τήν τε γὰρ Ναύπακτον ὁρμητήριον ἐπὶ τῇ Πελοποννήσῳ παρείχοντο καὶ τοὺς ἐν τῇ Σφακτηρίᾳ Σπαρτιατῶν ἀποληφθέντας Μεσσηνίων σφενδονῆται τῶν ἐκ Ναυπάκτου συνεξεῖλον.
From this time onward their hatred against the Lacedaemonians persisted, and they demonstrated their hostility most strongly during the war which broke out between the Peloponnesians and the Athenians; for they offered Naupactus as a base to operate against the Peloponnese, and Messenian slingers from Naupactus assisted in cutting off the Spartans who had been trapped on the island of Sphacteria.