Genesis 17:11-14

11You are to undergo circumcision, and it will be the sign of the covenant between me and you. 12For the generations to come every male among you who is eight days old must be circumcised, including those born in your household or bought with money from a foreigner—those who are not your offspring. 13Whether born in your household or bought with your money, they must be circumcised. My covenant in your flesh is to be an everlasting covenant. 14Any uncircumcised male, who has not been circumcised in the flesh, will be cut off from his people; he has broken my covenant.”