Genesis 15:12-16

And when the sun was going down, a deep sleep fell upon Abram; and, lo, an horror of great darkness fell upon him. And he said unto Abram, Know of a surety that thy seed shall be a stranger in a land that is not their's, and shall serve them; and they shall afflict them four hundred years; and also that nation, whom they shall serve, will I judge: and afterward shall they come out with great substance. And thou shalt go to thy fathers in peace; thou shalt be buried in a good old age. But in the fourth generation they shall come hither again: for the iniquity of the Amorites is not yet full.