19 But God said, No, but Sarah your wife will bear you a son, and you shall call his name Isaac; and I will establish My covenant with him for an everlasting covenant for his seed after him.
Genesis 21:3, 12
3 And Abraham called the name of his son who was born to him, whom Sarah bore to him, Isaac.
12 And God said the Abraham, Do not be displeased on account of the boy and on account of your maidservant. Whatever Sarah says to you, listen to her voice, for in Isaac shall your seed be called.
7 Neither is it that because they are the seed of Abraham, they are all children; but, "In Isaac shall your seed be called,"
8 That is, it is not the children of the flesh who are the children of God, but the children of the promise are accounted as the seed.
9 For this is the word of promise, "At this time next year I will come, and Sarah shall have a son."