Genesis 21:2-5

2And Sarah aconceived and bore Abraham a son in his old age bat the time of which God had spoken to him. 3Abraham called the name of his son who was born to him, whom Sarah bore him, cIsaac.
 Isaac means he laughs
4And Abraham ecircumcised his son Isaac when he was eight days old, fas God had commanded him. 5 gAbraham was a hundred years old when his son Isaac was born to him.
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