Genesis 15:9-13

9And he said unto him, Take me a heifer three years old, and a she-goat three years old, and a ram three years old, and a turtle-dove, and a young pigeon. 10And he took him all these, and divided them in the midst, and laid each half over against the other: but the birds divided he not. 11And the birds of prey came down upon the carcasses, and Abram drove them away.

12And when the sun was going down, a deep sleep fell upon Abram; and, lo, a horror of great darkness fell upon him. 13And he said unto Abram, Know of a surety that thy seed shall be sojourners in a land that is not theirs, and shall serve them; and they shall afflict them four hundred years;