Ezekiel 37:1

The (metaphorical) hand of G-d was on me and it carried me in the spirit of G-d, placing me down in a valley that was full of bones.

Rashi quotes the Talmud (Sanhedrin 92b) that these were the bones of members of the Tribe of Ephraim who miscalculated the time for the redemption from slavery and tried to leave Egypt before the appointed time. They were killed by the men of Gath, in an incident recorded in I Chronicles chapter 7.