Genesis 17:13 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.
Genesis 17:24-27 Abraham was ninety-nine years old when he was circumcised in the flesh of his foreskin. And Ishmael his son was thirteen years old when he was circumcised in the flesh of his foreskin. That very same day Abraham was circumcised, and his son Ishmael; and all the men of his house, born in the house or bought with money from a foreigner, were circumcised with him.
Genesis 21:4 Then Abraham circumcised his son Isaac when he was eight days old, as God had commanded him.