Genesis 17:11-13 New Revised Standard Version (NRSV)
11 You shall circumcise the flesh of your foreskins, and it shall be a sign of the covenant between me and you. 12 Throughout your generations every male among you shall be circumcised when he is eight days old, including the slave born in your house and the one bought with your money from any foreigner who is not of your offspring. 13 Both the slave born in your house and the one bought with your money must be circumcised. So shall my covenant be in your flesh an everlasting covenant.