Genesis 21:8-13

The child [Isaac] grew and was weaned, and Abraham held a great feast on the day that Isaac was weaned. Now [as time went on] Sarah saw [Ishmael] the son of Hagar the Egyptian, whom she had borne to Abraham, mocking [Isaac]. [Gal 4:29] Therefore she said to Abraham, “Drive out this maid and her son, for the son of this maid shall not be an heir with my son Isaac.” [Gal 4:28-31] The situation distressed Abraham greatly because of his son [Ishmael]. God said to Abraham, “Do not let it distress you because of Ishmael and your maid; whatever Sarah tells you, listen to her and do what she asks, for your descendants will be named through Isaac. [Rom 9:7] And I will also make a nation of [Ishmael] the son of the maid, because he is your descendant.”