Eli Yassif of Haaretz has a recent article that looks at legends surrounding the ten Lost Tribes of Israel. One story, found in the book of 4 Esdras, speaks of the ten tribes being “carried over the waters” and inhabiting a land “where never mankind dwelt.”
As far as we know, the oldest source that refers to the myth is the Fourth Book of Esdras from the Jewish Apocrypha, written shortly after the destruction of the Second Temple in Jerusalem, toward the end of the 1st century C.E. This tradition interprets one of the central visions described in 2 Esdras 13:40-48 (King James Version): “Those are the ten tribes, which were carried away prisoners out of their own land in the time of Osea the king, whom Salmanasar the king of Assyria led away captive, and he carried them over the waters, and so came they into another land. But they took this counsel among themselves, that they would leave the multitude of the heathen, and go forth into a further country, where never mankind dwelt, that they might there keep their statutes, which they never kept in their own land. And they entered into Euphrates by the narrow places of the river. For the most High then shewed signs for them, and held still the flood, till they were passed over. For through that country there was a great way to go, namely, of a year and a half; and the same region is called Arsareth … But those that be left behind of thy people are they that are found within my borders.”
It is interesting to see the speculation in this early Jewish text on where the tribes had been taken.