Genesis 17:19-21

19God said to Abraham, ‘No, your wife Sarah will give birth to a son for you. You must give him the name “Isaac”. I will make my covenant with him and with his descendants for all time.

20I have heard what you want me to do for Ishmael. I will bless him. I will cause him to have many descendants. Among his descendants there will be 12 rulers. His descendants will become a great nation.

21But I will make my covenant with Isaac, not with Ishmael. At about this time next year, Sarah will give birth to your son, Isaac.’