Abraham named his son Isaac, the son Sarah gave birth to.
He circumcised Isaac when he was eight days old as God had commanded.
Abraham was one hundred years old when his son Isaac was born.
And Sarah said, "God has made me laugh. Everyone who hears about this will laugh with me.
No one thought that I would be able to have Abraham's child, but even though Abraham is old I have given him a son."
Isaac grew, and when he became old enough to eat food, Abraham gave a great feast.
But Sarah saw Ishmael making fun of Isaac. (Ishmael was the son of Abraham by Hagar, Sarah's Egyptian slave.)
So Sarah said to Abraham, "Throw out this slave woman and her son. Her son should not inherit anything; my son Isaac should receive it all."
This troubled Abraham very much because Ishmael was also his son.
But God said to Abraham, "Don't be troubled about the boy and the slave woman. Do whatever Sarah tells you. The descendants I promised you will be from Isaac.
I will also make the descendants of Ishmael into a great nation because he is your son, too."