Abraham named him Isaac,
and when Isaac was eight days old, Abraham circumcised him, as God had commanded. 1
References for Genesis 21:4
21.4 Gn 17.12; Ac 7.8.
Abraham was a hundred years old when Isaac was born.
Sarah said, "God has brought me joy and laughter. Everyone who hears about it will laugh with me."
References for Genesis 21:6
Then she added, "Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age."
The child grew, and on the day that he was weaned, Abraham gave a great feast.
One day Ishmael, whom Hagar the Egyptian had borne to Abraham, was playing with Sarah's son Isaac.
References for Genesis 21:9
Sarah saw them and said to Abraham, "Send this slave and her son away. The son of this woman must not get any part of your wealth, which my son Isaac should inherit." 2
References for Genesis 21:10
21.10 Ga 4.29, 30.
This troubled Abraham very much, because Ishmael also was his son.
But God said to Abraham, "Don't be worried about the boy and your slave Hagar. Do whatever Sarah tells you, because it is through Isaac that you will have the descendants I have promised. 3
References for Genesis 21:12
21.12 Ro 9.7; He 11.18.
I will also give many children to the son of the slave woman, so that they will become a nation. He too is your son."