Herodotus 1.165.3 (tr. A.D. Godley):
Not only so, but they sank in the sea a mass of iron, and swore never to return to Phocaea before the iron should again appear. But while they prepared to voyage to Cyrnus, more than half of the citizens were taken with a longing and a pitiful sorrow for the city and the life of their land, and they broke their oath and sailed back to Phocaea.
πρὸς δὲ ταύτῃσι καὶ μύδρον σιδήρεον κατεπόντωσαν καὶ ὤμοσαν μὴ πρὶν ἐς Φωκαίην ἥξειν πρὶν ἢ τὸν μύδρον τοῦτον ἀναφανῆναι. στελλομένων δὲ αὐτῶν ἐπὶ τὴν Κύρνον, ὑπερημίσεας τῶν ἀστῶν ἔλαβε πόθος τε καὶ οἶκτος τῆς πόλιος καὶ τῶν ἠθέων τῆς χώρης, ψευδόρκιοι δὲ γενόμενοι ἀπέπλεον ὀπίσω ἐς τὴν Φωκαίην.