Genesis
Chapters 21:1-4
King James Version, American Edition
1And the Lord visited Sarah as he had said, and the Lord did unto Sarah as he had spoken.
2For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.
3And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.
4And Abraham circumcised his son Isaac being eight days old, as God had commanded him.