Genesis 17:21 (KJV)

And I will bless her, and give thee a son also of her: yea, I will bless her, and she shall be a mother of nations; kings of people shall be of her.

Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear?

And Abraham said unto God, O that Ishmael might live before thee!

And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him.

And as for Ishmael, I have heard thee: Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation.

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.