Genesis 17:10-12

17:10 This is my requirement that you and your descendants after you must keep: Every male among you must be circumcised. 17:11 You must circumcise the flesh of your foreskins. This will be a reminder of the covenant between me and you. 17:12 Throughout your generations every male among you who is eight days old must be circumcised, whether born in your house or bought with money from any foreigner who is not one of your descendants.