Passage 9.26.4
οὐκ ἔχοντας δὲ αὐτοὺς ἀποκρίνασθαι θανάτῳ ζημιοῦν, ἅτε οὐ προσηκόντως ἀμφισβητοῦντας γένους τε καὶ ἀρχῆς. Οἰδίπους δὲ ἄρα ἀφίκετο ὑπὸ ὀνείρατος δεδιδαγμένος τὸν χρησμόν.
Since they could not answer, they punished them with death, on the grounds that they had improperly disputed their lineage and royal power. Oedipus, it is said, arrived, having learned of the oracle through a dream.