Genesis 17:10-13

This is my covenant, which ye shall keep, between me and you and thy seed after thee: every male among you shall be circumcised. And ye shall be circumcised in the flesh of your foreskin; and it shall be a token of a covenant betwixt me and you. And he that is eight days old shall be circumcised among you, every male throughout your generations, he that is born in the house, or bought with money of any foreigner that is not of thy seed. He that is born in thy house, and he that is bought with thy money, must needs be circumcised: and my covenant shall be in your flesh for an everlasting covenant.