Genesis 21:1-7 - The Birth Of Isaac
1 And the Lord came to Sarah as he had said and did to her as he had undertaken. 2 And Sarah became with child, and gave Abraham a son when he was old, at the time named by God. 3 And Abraham gave to his son, to whom Sarah had given birth, the name Isaac. 4 And when his son Isaac was eight days old, Abraham made him undergo circumcision, as God had said to him. 5 Now Abraham was a hundred years old when the birth of Isaac took place.
6 And Sarah said, God has given me cause for laughing, and everyone who has news of it will be laughing with me. 7 And she said, Who would have said to Abraham that Sarah would have a child at her breast? for see, I have given him a son now when he is old.