Passage 10.29.2
τὰ οὖν ἐς τοῦ Ὄκνου τὴν γυναῖκα ἐθέλουσιν αἰνίξασθαι τὸν Πολύγνωτον. οἶδα δὲ καὶ ὑπὸ Ἰώνων, ὁπότε ἴδοιέν τινα πονοῦντα ἐπὶ οὐδενὶ ὄνησιν φέροντι, ὑπὸ τούτων εἰρημένον ὡς ὁ ἀνὴρ οὗτος συνάγει τοῦ Ὄκνου τὴν θώμιγγα. ὄκνον δʼ οὖν καὶ μάντεων οἱ ὁρῶντες τοὺς οἰωνοὺς καλοῦσί τινα ὄρνιθα· καὶ ἔστιν οὗτος ὁ ὄκνος μέγιστος μὲν καὶ κάλλιστος ἐρωδιῶν, εἰ δὲ ἄλλος τις ὀρνίθων σπάνιός ἐστι καὶ οὗτος.
Thus regarding the woman of Oknos, they want to suggest that Polygnotos is speaking allegorically. Indeed I know that the Ionians, whenever they see someone laboring at work which brings no profit whatsoever, say of him, “this man is weaving the rope of Oknos.” Moreover, the bird watchers among the seers also call a certain bird "oknos." This "oknos" is the largest and most beautiful species of heron, and if there is any other exceptionally rare bird, this one too is rare.