Genesis 17:9-13

9God also said to Abraham, “As for you, you and your offspring after you throughout their generations are to keep my covenant.

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.

13Whether born in your household or purchased, he must be circumcised. My covenant will be marked in your flesh as a permanent covenant.