Genesis 17:9-14 (New King James Version)

⁹ And God said to Abraham: “As for you, you shall keep My covenant, you and your descendants after you throughout their generations. ¹⁰ This is My covenant which you shall keep, between Me and you and your descendants after you: Every male child among you shall be circumcised; ¹¹ and you shall be circumcised in the flesh of your foreskins, and it shall be a sign of the covenant between Me and you. ¹² He who is eight days old among you shall be circumcised, every male child in your generations, he who is born in your house or bought with money from any foreigner who is not your descendant. ¹³ He who is born in your house and he who is bought with your money must be circumcised, and My covenant shall be in your flesh for an everlasting covenant. ¹⁴ And the uncircumcised male child, who is not circumcised in the flesh of his foreskin, that person shall be cut off from his people; he has broken My covenant.”