Do what Sarah told you to do. Your seed will be Isaac's seed.
Abraham does what he's told
14 Abraham gave Hagar some bread and a bottle of water and sent her and Ishmael into the wilderness. 15 After the water ran out, Hagar put the little boy under a bush. 16 Then she went away, and said, "Let me not see his death." And she sat and wept.
17 God heard the little boy crying, and an angel called to Hagar from heaven, saying,
What's wrong with you, Hagar?
Don't be afraid. God has heard the voice of your little boy.
18 Get up and lift him up in your hand. I will make him a great nation.
19 God opened Hagar's eyes so she could see a well. And she gave Ishmael a drink. 20 Ishmael lived in the wilderness and became an archer. 21 And Hagar found an Egyptian wife for him to marry.
A few more words about this episode
Ishmael isn't mentioned by name in the text of Genesis 22. Instead, he is referred to as "the son of Hagar the Egyptian" (v.9), "the son of this bondwoman" (v.10), "the lad" (vv.12, 17-20), or "the child" (vv.14-26). But I used Ishmael's name in my summary of the text for the sake of clarity.
The Bible doesn't say much about Ishmael's life after he was abandoned by Abraham and Sarah, except to say that he died when he was 137 years old (Genesis 25:17).
Muslims believe that Ishmael, not Isaac, was the son that Allah told Abraham to sacrifice. And that Abraham and Ishmael traveled to Mecca to create the Kabba.
Sarah conceived and delivered a son (v.2)
God-assisted conceptions never result in daughters.
Sarah saw Ishmael mocking his little brother, Isaac (v.9)
What did Sarah see that disturbed her so much?
Jonathan Kirsch suggests in The Harlot by the Side of the Road that the "play" between Isaac and Ishmael may have been of a sexual nature, noting that the same word is used in Gen 26:8 to describe Isaac's fondling of Rebekah.