Sarah knew of God's promise to her and to Abraham that they would be parents to a new nation, but she grew to be an old woman, ninety-nine years old, and she still didn't have any children! One day, Abraham invited three travelers to dinner; hospitality was very important in the land where Abraham and Sarah pitched their tent because there weren't any restaurants to feed travelers. Sarah began immediately to bake fresh bread for these visitors, who were actually angels of the Lord. As she was working, she overheard one of the strangers say to Abraham, "I shall visit you again next year, and your wife will then have a son." Sarah laughed out loud when she heard that, because she was too old to have children, but the stranger insisted it was true. And sure enough, within the year Sarah gave birth to a son. She and Abraham named him Isaac, which in Hebrew means "laughter."
Genesis 18:1-15 and 21:1-7