Passage 10.38.2
οἱ δὲ Νέσσον πορθμεύοντα ἐπὶ τῷ Εὐήνῳ τρωθῆναι μὲν ὑπὸ Ἡρακλέους, οὐ μέντοι καὶ αὐτίκα γε ἀποθανεῖν ἀλλὰ ἐς τὴν γῆν ταύτην ἐκφυγεῖν νομίζουσι, καὶ ὡς ἀπέθανε σήπεσθαί τε ἄταφον καὶ ὀσμῆς τῷ ἐνταῦθα ἀέρι μεταδοῦναι δυσώδους. ὁ δὲ τρίτος τῶν λόγων καὶ ὁ τέταρτος, ὁ μὲν ποταμοῦ τινος ἄτοπον τήν τε ἀτμίδα καὶ αὐτό φησιν εἶναι τὸ ὕδωρ, ὁ δὲ τὸν ἀσφόδελον φύεσθαι πολὺν καὶ ἀνθοῦντα ὑπὸ τῆς ὀσμῆς.
Others consider that Nessus, after being wounded by Heracles while ferrying across the river Evenus, did not die immediately, but escaped instead to this land, and that when he died here his body rotted unburied and imparted a foul stench to the air there. The third and fourth accounts—one states that the unpleasant vapor and water itself come from a nearby river, whereas the other attributes the smell to a great quantity of blooming asphodel growing there.