Passage 4.19.2
τούτους παρὰ τῶν κατασκόπων πυνθανόμενος ὁ Ἀριστομένης τῇ πορείᾳ τε ἀτακτότερον χρῆσθαι καὶ ταῖς στρατοπεδείαις ἀφυλάκτως, ἐπιτίθεται νύκτωρ σφίσι· καὶ τῶν τε ἄλλων καθευδόντων ἔτι ἐφόνευσε τοὺς πολλοὺς καὶ τοὺς ἡγεμόνας Ὑπερμενίδην καὶ Ἀχλαδαῖον καὶ Λυσίστρατον καὶ Σίδεκτον ἀποκτίννυσι. διαρπάσας δὲ καὶ τὴν σκηνὴν τὴν στρατηγίδα παρέστησεν εὖ εἰδέναι Σπαρτιάταις ὡς Ἀριστομένης καὶ οὐκ ἄλλος Μεσσηνίων ἐστὶν ὁ ταῦτα εἰργασμένος.
When Aristomenes learned from his scouts that they proceeded carelessly on the march and neglected their camps' defense, he attacked them by night. While most of them were still sleeping, he killed a great number, including their commanders Hypermenides, Achladaeus, Lysistratus, and Sidectus. After plundering the tent of the Spartan generals, he made it clear to the Spartans beyond doubt that it was Aristomenes and no other Messenian who had performed these deeds.