Passage 1.41.5
Πίνδαρος δὲ τούτοις τε κατὰ ταὐτὰ ἐποίησε καὶ γαμβρὸν τοῖς Διοσκούροις Θησέα εἶναι βουλόμενον ἁρπασθεῖσαν τὴν Ἑλένην διαφυλάξαι , ἐς ὃ ἀπελθεῖν αὐτὸν Πειρίθῳ τὸν λεγόμενον γάμον συμπράξοντα. ὅστις δὲ ἐγενεαλόγησε, δῆλον ὡς πολλὴν τοῖς Μεγαρεῦσι σύνοιδεν εὐήθειαν, εἴ γε Θησεὺς ἦν ἀπόγονος Πέλοπος· ἀλλὰ γὰρ τὸν ὄντα λόγον οἱ Μεγαρεῖς εἰδότες ἐπικρύπτουσιν, οὐ βουλόμενοι δοκεῖν ἁλῶναί σφισιν ἐπὶ τῆς ἀρχῆς τῆς Νίσου τὴν πόλιν, διαδέξασθαι δὲ τὴν βασιλείαν γαμβρὸν Νίσου τε Μεγαρέα καὶ αὖθις Ἀλκάθουν Μεγαρέως.
Pindar relates these matters similarly, stating also that Theseus, wishing to be related to the Dioscuri by marriage, carried off Helen and kept watch over her until he departed to join Peirithous in his celebrated bridal expedition. Yet whoever devised this genealogy evidently relied greatly upon the simplicity of the Megarians, if indeed Theseus were a descendant of Pelops. Actually the Megarians, though aware of the true account, conceal it, unwilling to admit that their city fell to hostile capture during the rule of Nisus, and preferring instead the story of its succession passing legitimately from Nisus to his son-in-law Megareus, and subsequently from Megareus to Alcathous.