Genesis 17:10-14

10This is my covenant, which you shall keep, between me and you and your offspring after you: Every male among you shall be circumcised. 11You shall be circumcised in the flesh of your foreskins, and it shall be a sign of the covenant between me and you. 12He who is eight days old among you shall be circumcised. Every male throughout your generations, whether born in your house or bought with your money from any foreigner who is not of your offspring, 13both he who is born in your house and he who is bought with your money, shall surely be circumcised. So shall my covenant be in your flesh an everlasting covenant. 14Any uncircumcised male who is not circumcised in the flesh of his foreskin shall be cut off from his people; he has broken my covenant.”