The Lord appeared to Abraham by the oaks of Mamre as he sat at the entrance of his tent in the heat of the day. Abraham welcomed the Lord and his two angels, insisting they wash their feet and rest under a tree while he brought them a morsel of bread. The Lord told Abraham that he would surely return to him about this time next year, and Sarah laughed to herself at the idea of her and Abraham, being very old, having a child together.

1. Genesis 18:1-15
Sarah Laughs