Genesis 15:8-12

And he said, Lord GOD, whereby shall I know that I shall inherit it?

And he said unto him, Take me an heifer of three years old, and a she goat of three years old, and a ram of three years old, and a turtledove, and a young pigeon.

And he took unto him all these, and divided them in the midst, and laid each piece one against another: but the birds divided he not.

And when the fowls came down upon the carcases, Abram drove them away.

And when the sun was going down, a deep sleep fell upon Abram; and, lo, an horror of great darkness fell upon him.