Genesis 18:1-15
Now the Lord appeared to him by the oaks of Mamre, while he was sitting at the tent door in the heat of the day. When he lifted up his eyes and looked, behold, three men were standing opposite him; and when he saw them, he ran from the tent door to meet them and bowed himself to the earth, and said, “My Lord, if now I have found favor in Your sight, please do not pass Your servant by. Please let a little water be brought and wash your feet, and rest yourselves under the tree; and I will bring a piece of bread, that you may refresh yourselves; after that you may go on, since you have visited your servant.” And they said, “So do, as you have said.” So Abraham hurried into the tent to Sarah, and said, “Quickly, prepare three measures of fine flour, knead it and make bread cakes.” Abraham also ran to the herd, and took a tender and choice calf and gave it to the servant, and he hurried to prepare it. He took curds and milk and the calf which he had prepared, and placed it before them; and he was standing by them under the tree as they ate.
Then they said to him, “Where is Sarah your wife?” And he said, “There, in the tent.” He said, “I will surely return to you at this time next year; and behold, Sarah your wife will have a son.” And Sarah was listening at the tent door, which was behind him. Now Abraham and Sarah were old, advanced in age; Sarah was past childbearing. Sarah laughed to herself, saying, “After I have become old, shall I have pleasure, my lord being old also?” And the Lord said to Abraham, “Why did Sarah laugh, saying, ‘Shall I indeed bear a child, when I am so old?’ Is anything too difficult for the Lord? At the appointed time I will return to you, at this time next year, and Sarah will have a son.” Sarah denied it however, saying, “I did not laugh”; for she was afraid. And He said, “No, but you did laugh.”
Genesis 21:1-8
Then the Lord took note of Sarah as He had said, and the Lord did for Sarah as He had promised. So Sarah conceived and bore a son to Abraham in his old age, at the appointed time of which God had spoken to him. Abraham called the name of his son who was born to him, whom Sarah bore to him, Isaac.Then Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. Now Abraham was one hundred years old when his son Isaac was born to him. Sarah said, “God has made laughter for me; everyone who hears will laugh with me.” And she said, “Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.”
The child grew and was weaned, and Abraham made a great feast on the day that Isaac was weaned.