Genesis 17:12-22

12 Throughout your generations every male among you shall be circumcised when he is eight days old, including the slave born in your house and the one bought with your money from any foreigner who is not of your offspring.
13 Both the slave born in your house and the one bought with your money must be circumcised. So shall my covenant be in your flesh an everlasting covenant.
14 Any uncircumcised male who is not circumcised in the flesh of his foreskin shall be cut off from his people; he has broken my covenant."
15 God said to Abraham, "As for Sarai your wife, you shall not call her Sarai, but Sarah shall be her name.
16 I will bless her, and moreover I will give you a son by her. I will bless her, and she shall give rise to nations; kings of peoples shall come from her."
17 Then Abraham fell on his face and laughed, and said to himself, "Can a child be born to a man who is a hundred years old? Can Sarah, who is ninety years old, bear a child?"
18 And Abraham said to God, "O that Ishmael might live in your sight!"
19 God said, "No, but your wife Sarah shall bear you a son, and you shall name him Isaac. I will establish my covenant with him as an everlasting covenant for his offspring after him.
20 As for Ishmael, I have heard you; I will bless him and make him fruitful and exceedingly numerous; he shall be the father of twelve princes, and I will make him a great nation.
21 But my covenant I will establish with Isaac, whom Sarah shall bear to you at this season next year."
22 And when he had finished talking with him, God went up from Abraham.