Passage 6.20.16
Ἕλληνες δὲ οὐ κατὰ τὰ αὐτὰ νομίζουσιν ἐς τὸν Ταράξιππον, ἀλλʼ οἱ μὲν εἶναι τάφον ἀνδρὸς αὐτόχθονος καὶ ἀγαθοῦ τὰ ἐς ἱππικήν--- καὶ ὄνομα Ὠλένιον αὐτῷ τίθενται, ἀπὸ τούτου δὲ καὶ τὴν Ὠλενίαν ἐν τῇ Ἠλείᾳ πέτραν φασὶν ὀνομασθῆναι---, οἱ δὲ τὸν Φλιοῦντος Δαμέωνα μετασχόντα Ἡρακλεῖ τῆς ἐπὶ Αὐγέαν καὶ Ἠλείους στρατείας αὐτόν τε ἀποθανεῖν καὶ τὸν ἵππον ἐφʼ ᾧ ἐπωχεῖτο ὑπὸ Κτεάτου λέγουσι τοῦ Ἄκτορος, καὶ τὸ μνῆμα κοινὸν Δαμέωνι καὶ τῷ ἵππῳ γενέσθαι.
The Greeks, however, do not agree in their beliefs about Taraxippos. Some say it is the tomb of a native-born hero, excellent in horsemanship, giving him the name Olenios. From him, they say, the Olenian rock in Elis also takes its name. Others say he is Dameon of Phlius, who accompanied Herakles in his expedition against Augeas and the Eleans; according to them, Dameon himself was killed, along with the horse he rode, by Kteatos the son of Aktor, and a common tomb was made for Dameon and his horse.