Passage 9.29.1
ταῦτα μὲν δὴ ἔχοντά ἐστιν οὕτω, θῦσαι δὲ ἐν Ἑλικῶνι Μούσαις πρώτους καὶ ἐπονομάσαι τὸ ὄρος ἱερὸν εἶναι Μουσῶν Ἐφιάλτην καὶ Ὦτον λέγουσιν, οἰκίσαι δὲ αὐτοὺς καὶ Ἄσκρην· καὶ δὴ καὶ Ἡγησίνους ἐπὶ τῷδε ἐν τῇ Ἀτθίδι ἐποίησεν, Ἄσκρῃ δʼ αὖ παρέλεκτο Ποσειδάων ἐνοσίχθων, ἣ δή οἱ τέκε παῖδα περιπλομένων ἐνιαυτῶν Οἴοκλον, ὃς πρῶτος μετʼ Ἀλωέος ἔκτισε παίδων Ἄσκρην, ἥ θʼ Ἑλικῶνος ἔχει πόδα πιδακόεντα. Hegesinus Atthis, unknown location.
These things then stand thus. It is said that Ephialtes and Otus were the first to sacrifice to the Muses at Helicon, and to name the mountain sacred to the Muses. They are also said to have founded Ascra. Indeed, Hegesinus makes mention of this in his poem "Atthis": "To Ascra too did earthquake-shaking Poseidon lie nearby, who bore to him a son in revolving years, Oeoclus, who was first after Aloeus’ children to found Ascra, which rests at Helicon's spring-rich foot."