Genesis 17:19-22

But God replied, “No—Sarah, your wife, will give birth to a son for you. You will name him Isaac, and I will confirm my covenant with him and his descendants as an everlasting covenant. As for Ishmael, I will bless him also, just as you have asked. I will make him extremely fruitful and multiply his descendants. He will become the father of twelve princes, and I will make him a great nation. But my covenant will be confirmed with Isaac, who will be born to you and Sarah about this time next year.” When God had finished speaking, he left Abraham.