Genesis 17:1-4, 17-19

And when Abram was ninety years old and nine, the LORD appeared to Abram, and said unto him, I am the Almighty God; walk before me, and be thou perfect. And I will make my covenant between me and thee, and will multiply thee exceedingly. And Abram fell on his face: and God talked with him, saying, As for me, behold, my covenant is with thee, and thou shalt be a father of many nations.

Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear? And Abraham said unto God, O that Ishmael might live before thee! And God said, Sarah thy wife shall bear thee a son indeed; and thou shalt call his name Isaac: and I will establish my covenant with him for an everlasting covenant, and with his seed after him.