Genesis 15:9-13

9And he said to him, Take me an heifer of three years old, and a female goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon. 10And he took to him all these, and divided them in the midst, and laid each piece one against another: but the birds he did not divide. 11And when the fowls came down upon the carcases, Abram drove them away.

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