Genesis 17:10-12

10This is my covenant between me and you and your offspring after you, which you are to keep: Every one of your males must be circumcised.

11You must circumcise the flesh of your foreskin to serve as a sign of the covenant between me and you.

12Throughout your generations, every male among you is to be circumcised at eight days old — every male born in your household or purchased from any foreigner and not your offspring.