Genesis 15:12-16

As the sun was going down, Abram fell into a deep sleep, and a terrifying darkness came down over him. Then the LORD said to Abram, “You can be sure that your descendants will be strangers in a foreign land, where they will be oppressed as slaves for 400 years. But I will punish the nation that enslaves them, and in the end they will come away with great wealth. (As for you, you will die in peace and be buried at a ripe old age.) After four generations your descendants will return here to this land, for the sins of the Amorites do not yet warrant their destruction.”