Genesis 15:12-16

As the sun was about to set, a deep sleep fell upon Abram, and a great, dark dread descended upon him. Then the LORD said to Abram: Know for certain that your descendants will reside as aliens in a land not their own, where they shall be enslaved and oppressed for four hundred years. But I will bring judgment on the nation they must serve, and after this they will go out with great wealth. You, however, will go to your ancestors in peace; you will be buried at a ripe old age. In the fourth generation your descendants will return here, for the wickedness of the Amorites is not yet complete.