Passage 5.8.3
ἔθηκε δὲ καὶ Αὐγέας καὶ Ἡρακλῆς ὁ Ἀμφιτρύωνος ἑλὼν Ἦλιν· ὁπόσους δὲ ἐστεφάνωσεν οὗτος νικῶντας, ἔστιν Ἰόλαος ταῖς Ἡρακλέους δραμὼν ἵπποις. ἦν δὲ ἄρα ἐκ παλαιοῦ καθεστηκὸς ἀγωνίζεσθαι καὶ ἀλλοτρίαις ἵπποις· Ὅμηρος γοῦν ἐν ἄθλοις τεθεῖσιν ἐπὶ Πατρόκλῳ πεποίηκεν ὡς Μενέλαος Αἴθῃ τῇ Ἀγαμέμνονος, τῷ δὲ ἑτέρῳ χρήσαιτο τῶν ἵππων οἰκείῳ.
Augeas also established competitions, as did Heracles, son of Amphitryon, after conquering Elis. Among the victors crowned by him was Iolaus, who raced driving the horses belonging to Heracles. From ancient times indeed, it was an established practice to compete even with horses belonging to another. Homer, for example, in describing the games organized in honor of Patroclus, relates how Menelaus competed with Agamemnon's mare Aethe, while the other horse yoked with her was his own.