Genesis 15:13-17

Then God said to Abram, “Know for certain that your descendants will be strangers in a land that is not theirs, where they will be enslaved and oppressed for four hundred years.

But I will also judge the nation whom they will serve, and afterward they will come out with many possessions.

As for you, you shall go to your fathers in peace; you will be buried at a good old age.

Then in the fourth generation they will return here, for the wrongdoing of the Amorite is not yet complete.”

Now it came about, when the sun had set, that it was very dark, and behold, a smoking oven and a flaming torch appeared which passed between these pieces.