Genesis 15:11-13

And when the fowls came down upon the carcases, Abram drove them away.

¶ 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 theirs, and shall serve them; and they shall afflict them four hundred years;