Genesis 17:15-27 NIV
God also said to Abraham, “As for Sarai your wife, you are no longer to call her Sarai; her name will be Sarah. I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her.”
Abraham fell facedown; he laughed and said to himself, “Will a son be born to a man a hundred years old? Will Sarah bear a child at the age of ninety?” And Abraham said to God, “If only Ishmael might live under your blessing!”
Then God said, “Yes, but your wife Sarah will bear you a son, and you will call him Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him. And as for Ishmael, I have heard you: I will surely bless him; I will make him fruitful and will greatly increase his numbers. He will be the father of twelve rulers, and I will make him into a great nation. But my covenant I will establish with Isaac, whom Sarah will bear to you by this time next year.” When he had finished speaking with Abraham, God went up from him.
On that very day Abraham took his son Ishmael and all those born in his household or bought with his money, every male in his household, and circumcised them, as God told him. Abraham was ninety-nine years old when he was circumcised, and his son Ishmael was thirteen; Abraham and his son Ishmael were both circumcised on that very day. And every male in Abraham’s household, including those born in his household or bought from a foreigner, was circumcised with him.
NIV: New International Version