Abraham named his son—the one Sarah bore him—Isaac.
References for Genesis 21:3
Abraham circumcised his son Isaac when he was eight days old just as God had commanded him.
Abraham was 100 years old when his son Isaac was born.
Sarah said, "God has given me laughter. Everyone who hears about it will laugh with me."
References for Genesis 21:6
She said, "Who could have told Abraham that Sarah would nurse sons? But now I've given birth to a son when he was old!"
The boy grew and stopped nursing. On the day he stopped nursing, Abraham prepared a huge banquet.
References for Genesis 21:8
Sarah saw Hagar's son laughing, the one Hagar the Egyptian had borne to Abraham.
So she said to Abraham, "Send this servant away with her son! This servant's son won't share the inheritance with my son Isaac."
This upset Abraham terribly because the boy was his son.
God said to Abraham, "Don't be upset about the boy and your servant. Do everything Sarah tells you to do because your descendants will be traced through Isaac.
But I will make of your servant's son a great nation too, because he is also your descendant."