Genesis 21:2-12

2 Sarah conceived, and bore Avraham a son in his old age, at the set time of which God had spoken to him.
3 Avraham called his son who was born to him, whom Sarah bare to him, Yitzchak.
4 Avraham circumcised his son, Yitzchak, when he was eight days old, as God had commanded him.
5 Avraham was one hundred years old when his son, Yitzchak, was born to him.
6 Sarah said, "God has made me laugh. Everyone who hears will laugh with me."
7 She said, "Who would have said to Avraham, that Sarah would nurse children? For I have borne him a son in his old age."
8 The child grew, and was weaned. Avraham made a great feast on the day that Yitzchak was weaned.
9 Sarah saw the son of Hagar the Mitzrian, whom she had borne to Avraham, mocking.
10 Therefore she said to Avraham, "Cast out this handmaid and her son! For the son of this handmaid will not be heir with my son, even with Yitzchak."
11 The thing was very grievous in Avraham's sight on account of his son.
12 God said to Avraham, "Don't let it be grievous in your sight because of the boy, and because of your handmaid. In all that Sarah says to you, listen to her voice. For from Yitzchak will your seed be called.