Genesis 17:9-14

Then God said to Abraham, “You and your descendants must keep this agreement from now on. This is my agreement with you and all your descendants, which you must obey: Every male among you must be circumcised. Cut away your foreskin to show that you are prepared to follow the agreement between me and you. From now on when a baby boy is eight days old, you will circumcise him. This includes any boy born among your people or any who is your slave, who is not one of your descendants. Circumcise every baby boy whether he is born in your family or bought as a slave. Your bodies will be marked to show that you are part of my agreement that lasts forever. Any male who is not circumcised will be cut off from his people, because he has broken my agreement.”