Genesis 17:9-14

God explained to Abraham, “Your part of the covenant is to obey its terms, you and your descendants throughout the ages. So here is the sign of the covenant that you are to keep, so that it will endure between you and me and your descendants: circumcise every male among you. You must undergo cutting off the flesh of your foreskin as a special sign of the covenant between me and you. Throughout your generations, each male child must be circumcised eight days after his birth. This includes those not of your descendants—those born in your household and foreign-born servants whom you have purchased; they must be circumcised, homeborn and purchased alike. In this way, you will carry in your flesh the sign of my everlasting covenant. Any uncircumcised male who does not have the foreskin of his flesh cut off will be cut off from his people, for he has broken my covenant.”