Genesis 15:8-11
8 But Abram said, “Sovereign Lord, how can I know that I will gain possession of it?” 9 So the Lord said to him, “Bring me a heifer, a goat and a ram, each three years old, along with a dove and a young pigeon.” 10 Abram brought all these to him, cut them in two and arranged the halves opposite each other; the birds, however, he did not cut in half. 11 Then birds of prey came down on the carcasses, but Abram drove them away.