Genesis 17:21-25

But my covenant will I establish with Isaac, which Sarah shall bear unto thee at this set time in the next year.

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.