Sarah laughs at the idea of bearing a son in old age
The Lord said, “I will surely return to you about this time next year, and Sarah your wife shall have a son.” And Sarah was listening at the tent door behind him.
Now Abraham and Sarah were old, advanced in years. The way of women had ceased to be with Sarah. So Sarah laughed to herself, saying, “After I am worn out, and my lord is old, shall I have pleasure?”
The Lord said to Abraham, “Why did Sarah laugh and say, ‘Shall I indeed bear a child, now that I am old?’ Is anything too hard for the Lord? At the appointed time I will return to you, about this time next year, and Sarah shall have a son.” But Sarah denied it, saying, “I did not laugh,” for she was afraid. He said, “No, but you did laugh.”
(Genesis 21)
Sarah bears Isaac to Abraham, making laughter for her
The LORD returned to Sarah as He had said and did as He promised. Sarah conceived and bore Isaac to Abraham. Abraham was 100 years old. Isaac was circumcised at 8 days old, and Sarah said, "God has made laughter for me; everyone who hears will laugh over me.” And, “Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age."
(Genesis 21)
Ishmael mocks Isaac with laughter
Abraham held a great feast on the day that Isaac was weaned, and Sarah saw that Hagar's son was laughing. She told Abraham, "Cast out this slave woman with her son, for the son of this slave woman shall not be heir with my son Isaac." It displeased Abraham, but he sent her away early in the morning.
(Genesis 21)