Exodus 13:11-13

“When GOD brings you into the land of the Canaanites, as he promised you and your fathers, and turns it over to you, you are to set aside the first birth out of every womb to GOD. Every first birth from your livestock belongs to GOD. You can redeem every first birth of a donkey if you want to by substituting a lamb; if you decide not to redeem it, you must break its neck.