SERACH
"And Moshe took the bones of Yosef with him, for he (Yosef) had made the B'nei Yisrael swear, saying when G-d will remember you (pokod yifkod ...), then you shall take my bones out with you" (13:19).
The Gemara in Sotah 13a asks how Moshe knew where Yosef (who died some hundred and thirty years earlier) was buried. In one of the answers, the Gemara relates how the people informed Moshe that Serach, the daughter of Asher, was still alive from those who came down to Egypt. So he went to ask her for the required information, and she showed him the exact spot where they had thrown Yosef's metal coffin into the Nile (precisely in order that B'nei Yisrael should never be able to retrieve it).
Tosfos there asks why Moshe needed to ask Serach bas Asher, when both Machir and Ya'ir, sons of Menasheh (grandsons of Yosef himself), who lived in the time of Yaacov Avinu, and who entered Eretz Yisrael, were available and could well have given him the information he wanted.
