GENESIS 17:9-14, 23-27 (KJV)

⁹And God said unto Abraham, Thou shalt keep my covenant therefore, thou, and thy seed after thee in their generations. ¹⁰This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised. ¹¹And ye shall circumcise the flesh of your foreskin; and it shall be a token of the covenant betwixt me and you. ¹²And he that is eight days old shall be circumcised among you, every man child in your generations, he that is born in the house, or bought with money of any stranger, which is not of thy seed. ¹³He 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. ¹⁴And the uncircumcised man child whose flesh of his foreskin is not circumcised, that soul shall be cut off from his people; he hath broken my covenant.

²³And Abraham took Yishmael his son, and all that were born in his house, and all that were bought with his money, every male among the men of Abraham’s house; and circumcised the flesh of their foreskin in the selfsame day, as God had said unto him. ²⁴And Abraham was ninety years old and nine, when he was circumcised in the flesh of his foreskin. ²⁵And Yishmael his son was thirteen years old, when he was circumcised in the flesh of his foreskin. ²⁶In the selfsame day was Abraham circumcised, and Yishmael his son. ²⁷And all the men of his house, born in the house, and bought with money of the stranger, were circumcised with him.

GENESIS 21:4 (KJV)

⁴And Abraham circumcised his son Yitzhaq being eight days old, as God had commanded him.