Genesis 15:15-18

You, however, will go to your ancestors in peace and live a full life. And after the fourth generation, your descendants will return here; for then the sin of the Amorites will be ripe for judgment.” When the sun had set, and it was very dark, there suddenly appeared a smoking firepot and a blazing torch that passed between the split carcasses. On that day, YAHWEH entered into covenant with Abram: “I have given this land to your descendants, from the Egyptian border to the great river Euphrates