Genesis 17:11-20

You must cut off the flesh of your foreskin as a sign of the covenant between me and you. From generation to generation, every male child must be circumcised on the eighth day after his birth. This applies not only to members of your family but also to the servants born in your household and the foreign-born servants whom you have purchased. All must be circumcised. Your bodies will bear the mark of my everlasting covenant. Any male who fails to be circumcised will be cut off from the covenant family for breaking the covenant.” Then God said to Abraham, “Regarding Sarai, your wife—her name will no longer be Sarai. From now on her name will be Sarah. And I will bless her and give you a son from her! Yes, I will bless her richly, and she will become the mother of many nations. Kings of nations will be among her descendants.” Then Abraham bowed down to the ground, but he laughed to himself in disbelief. “How could I become a father at the age of 100?” he thought. “And how can Sarah have a baby when she is ninety years old?” So Abraham said to God, “May Ishmael live under your special blessing!” 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.