Genesis 21:1-6 NKJV

1 And the Lord visited Sarah as He had said, and the Lord did for Sarah as He had spoken.
2 For Sarah conceived and bore Abraham a son in his old age, at the set time of which God had spoken to him.
3 And Abraham called the name of his son who was born to him--whom Sarah bore to him--Isaac.
4 Then Abraham circumcised his son Isaac when he was eight days old, as God had commanded him.
5 Now Abraham was one hundred years old when his son Isaac was born to him.
6 And Sarah said, "God has made me laugh, and all who hear will laugh with me."