Genesis 18:1-15 New Revised Standard Version (NRSV)
18 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. 2 He looked up and saw three men standing near him. When he saw them, he ran from the tent entrance to meet them, and bowed down to the ground. 3 He said, “My lord, if I find favor with you, do not pass by your servant. 4 Let a little water be brought, and wash your feet, and rest yourselves under the tree. 5 Let me bring a little bread, that you may refresh yourselves, and after that you may pass on—since you have come to your servant.” So they said, “Do as you have said.” 6 And Abraham hastened into the tent to Sarah, and said, “Make ready quickly three measures of choice flour, knead it, and make cakes.” 7 Abraham ran to the herd, and took a calf, tender and good, and gave it to the servant, who hastened to prepare it. 8 Then he took curds and milk and the calf that he had prepared, and set it before them; and he stood by them under the tree while they ate.
9 They said to him, “Where is your wife Sarah?” And he said, “There, in the tent.” 10 Then one said, “I will surely return to you in due season, and your wife Sarah shall have a son.” And Sarah was listening at the tent entrance behind him. 11 Now Abraham and Sarah were old, advanced in age; it had ceased to be with Sarah after the manner of women. 12 So Sarah laughed to herself, saying, “After I have grown old, and my husband is old, shall I have pleasure?” 13 The Lord said to Abraham, “Why did Sarah laugh, and say, ‘Shall I indeed bear a child, now that I am old?’ 14 Is anything too wonderful for the Lord? At the set time I will return to you, in due season, and Sarah shall have a son.” 15 But Sarah denied, saying, “I did not laugh”; for she was afraid. He said, “Oh yes, you did laugh.”
Genesis 21:1-7 New Revised Standard Version (NRSV)
21 The Lord dealt with Sarah as he had said, and the Lord did for Sarah as he had promised. 2 Sarah conceived and bore Abraham a son in his old age, at the time of which God had spoken to him. 3 Abraham gave the name Isaac to his son whom Sarah bore him. 4 And Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. 5 Abraham was a hundred years old when his son Isaac was born to him. 6 Now Sarah said, “God has brought laughter for me; everyone who hears will laugh with me.” 7 And she said, “Who would ever have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.”