Genesis 17:27 (KJV)

And he left off talking with him, and God went up from Abraham.

And Abraham took Ishmael 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.

And Abraham was ninety years old and nine, 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.

In the selfsame day was Abraham circumcised, and Ishmael his son.