Passage 5.14.6
μετὰ δὲ τοὺς κατειλεγμένους Ἀλφειῷ καὶ Ἀρτέμιδι θύουσιν ἐπὶ ἑνὸς βωμοῦ· τὸ δὲ αἴτιον τούτου παρεδήλωσε μέν που καὶ Πίνδαρος ἐν ᾠδῇ, γράφομεν δὲ καὶ ἡμεῖς ἐν τοῖς λόγοις τοῖς Λετριναίοις. τούτου δὲ οὐ πόρρω καὶ ἄλλος τῷ Ἀλφειῷ βωμὸς πεποίηται, παρὰ δὲ αὐτόν ἐστιν Ἡφαίστου· τοῦ δὲ Ἡφαίστου τὸν βωμόν εἰσιν Ἠλείων οἳ ὀνομάζουσιν Ἀρείου Διός· λέγουσι δὲ οἱ αὐτοὶ οὗτοι καὶ ὡς Οἰνόμαος ἐπὶ τοῦ βωμοῦ τούτου θύοι τῷ Ἀρείῳ Διί, ὁπότε τῶν Ἱπποδαμείας μνηστήρων καθίστασθαι μέλλοι τινὶ ἐς ἵππων ἅμιλλαν.
After those mentioned above, they sacrifice to Alpheios and Artemis upon a single altar. The reason for this has been made clear by Pindar somewhere in an ode; and I myself have also written about it in my account of the Letrinians. Not far from this altar stands another dedicated to Alpheios, and close beside it is one of Hephaistos. Some of the Eleans, however, call this altar of Hephaistos the altar of Ares Zeus. These same Eleans also say that Oinomaos offered sacrifice on this altar to Ares Zeus whenever he was about to contend in chariot-racing with one of Hippodameia's suitors.