Genesis 17:15-16, 18:10-15, 21:1-6 (NIV)
17:15-16 God also said to Abraham, “As for Sarai your wife, you are no longer to call her Sarai; her name will be Sarah. 16 I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her.”
18:10-15 Then one of them said, “I will surely return to you about this time next year, and Sarah your wife will have a son.”
Now Sarah was listening at the entrance to the tent, which was behind him. 11 Abraham and Sarah were already very old, and Sarah was past the age of childbearing. 12 So Sarah laughed to herself as she thought, “After I am worn out and my lord is old, will I now have this pleasure?”
13 Then the Lord said to Abraham, “Why did Sarah laugh and say, ‘Will I really have a child, now that I am old?’ 14 Is anything too hard for the Lord? I will return to you at the appointed time next year, and Sarah will have a son.”
15 Sarah was afraid, so she lied and said, “I did not laugh.”
But he said, “Yes, you did laugh.”
21:1-6 Now the Lord was gracious to Sarah as he had said, and the Lord did for Sarah what he had promised. 2 Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him. 3 Abraham gave the name Isaac to the son Sarah bore him. 4 When his son Isaac was eight days old, Abraham circumcised him, as God commanded him. 5 Abraham was a hundred years old when his son Isaac was born to him.
6 Sarah said, “God has brought me laughter, and everyone who hears about this will laugh with me.”