Passage 2.31.9
καθῆραι δέ φασιν Ὀρέστην καθαρσίοις καὶ ἄλλοις καὶ ὕδατι τῷ ἀπὸ τῆς Ἵππου κρήνης. ἔστι γὰρ καὶ Τροιζηνίοις Ἵππου καλουμένη κρήνη, καὶ ὁ λόγος ἐς αὐτὴν διαφόρως τῷ Βοιωτῶν ἔχει· Πηγάσῳ γὰρ τῷ ἵππῳ καὶ οὗτοι λέγουσι τὸ ὕδωρ ἀνεῖναι τὴν γῆν θιγόντι τοῦ ἐδάφους τῇ ὁπλῇ, Βελλεροφόντην δὲ ἐλθεῖν ἐς Τροιζῆνα γυναῖκα αἰτήσοντα Αἴθραν παρὰ Πιτθέως, πρὶν δὲ γῆμαι συμβῆναί οἱ φυγεῖν ἐκ Κορίνθου.
They say that Orestes was purified both by rites of purification and especially by the water from the Hippocrene spring. For also among the Troezenians there is a spring named Hippocrene, though the account about it differs from that of the Boeotians. They too say that the water burst forth from the ground when the horse Pegasus struck the soil with his hoof. But they claim Bellerophon came to Troezen in order to seek from Pittheus Aethra for a wife, yet before the marriage could take place it happened that he fled from Corinth.