Genesis 15:12-14

12As the sun was setting, Abram fell into a deep sleep, and a thick and dreadful darkness came over him. 13Then the LORD said to him, “Know for certain that for four hundred years your descendants will be strangers in a country not their own and that they will be enslaved and mistreated there. 14But I will punish the nation they serve as slaves, and afterward they will come out with great possessions.