Genesis 17:19-21

19God said, “No, but aSarah your wife shall bear you a son, and you shall call his name bIsaac.
 Isaac means he laughs
I will establish my covenant with him as an everlasting covenant for his offspring after him.
20As for Ishmael, I have heard you; behold, I have blessed him and will make him fruitful and dmultiply him greatly. He eshall father twelve princes, and fI will make him into a great nation. 21But gI will establish my covenant with Isaac, hwhom Sarah shall bear to you at this time next year.”

Genesis 21:12

12But God said to Abraham, “Be not displeased because of the boy and because of your slave woman. Whatever Sarah says to you, do as she tells you, for ithrough Isaac shall your offspring be named.
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