Passage 10.5.7
ἤκουσα δὲ καὶ ὡς ἄνδρες ποιμαίνοντες ἐπιτύχοιεν τῷ μαντείῳ, καὶ ἔνθεοί τε ἐγένοντο ὑπὸ τοῦ ἀτμοῦ καὶ ἐμαντεύσαντο ἐξ Ἀπόλλωνος. μεγίστη δὲ καὶ παρὰ πλείστων ἐς Φημονόην δόξα ἐστίν, ὡς πρόμαντις γένοιτο ἡ Φημονόη τοῦ θεοῦ πρώτη καὶ πρώτη τὸ ἑξάμετρον ᾖσεν. Βοιὼ δὲ ἐπιχωρία γυνὴ ποιήσασα ὕμνον Δελφοῖς ἔφη κατασκευάσασθαι τὸ μαντεῖον τῷ θεῷ τοὺς ἀφικομένους ἐξ Ὑπερβορέων τούς τε ἄλλους καὶ Ὠλῆνα· τοῦτον δὲ καὶ μαντεύσασθαι πρῶτον καὶ ᾄσαι πρῶτον τὸ ἑξάμετρον.
I have also heard that men who were tending flocks chanced upon the oracle, and having become inspired by the vapor, they prophesied words from Apollo himself. However, the greatest and most widely held tradition concerns Phemonoe: it is said that she became the god's first prophetess, and was the first to sing her prophecies in hexameter verse. But according to Boeo, a local woman who composed a hymn for the Delphians, the oracle was established for Apollo by visitors from the Hyperboreans, among whom was Olen. She asserts that Olen was the very first to prophesy and the first to sing in hexameter verse.