Passage 4.6.4
Μύρωνα δὲ ἐπί τε ἄλλοις καταμαθεῖν ἔστιν οὐ προορώμενον εἰ ψευδῆ τε καὶ οὐ πιθανὰ δόξει λέγειν καὶ οὐχ ἥκιστα ἐν τῇδε τῇ Μεσσηνίᾳ συγγραφῇ. πεποίηκε γὰρ ὡς ἀποκτείνειε Θεόπομπον τῶν Λακεδαιμονίων τὸν βασιλέα Ἀριστομένης ὀλίγον πρὸ τῆς Ἀριστοδήμου τελευτῆς· Θεόπομπον δὲ οὔτε μάχης γινομένης οὔτε ἄλλως προαποθανόντα ἴσμεν πρὶν ἢ διαπολεμηθῆναι τὸν πόλεμον.
One can observe in other passages also that Myron was not concerned beforehand whether his statements might seem false and improbable, and not least in this work on Messenia. For he made Aristomenes slay Theopompus, the king of the Lacedaemonians, somewhat before the death of Aristodemus. But we know that Theopompus did not die beforehand, either in battle or otherwise, until the war had completely ended.