Genesis 17:12–14
12 He who is aeight days old among you shall be circumcised. Every male throughout your generations, whether born in your house or bbought with your money from any foreigner who is not of your offspring, 13 both he who is born in your house and he who is bought with your money, shall surely be circumcised. So shall my covenant be in your flesh an everlasting covenant. 14 Any uncircumcised male who is not circumcised in the flesh of his foreskin shall be cut off from his people; he has broken my covenant.”
Genesis 21:4
4 And Abraham pcircumcised his son Isaac when he was eight days old, qas God had commanded him.