Sarah laughed

Gen. 18:11] Abraham and Sarah were old, well advanced in years; the way of women had ceased for Sarah --- 12] so Sarah laughed inwardly, thinking: "Now that I am withered, will I have pleasure, with my lord so old!" 13] But the Eternal One said to Abraham, "Why is Sarah laughing so, thinking: 'Am I really going to bear a child, when I have grown so old?' 14] Is any wonder too difficult for the Eternal? At this fixed time, next year, I will return to you, and Sarah shall have a son. 14] Sarah, then denied it, for she was afraid, and said, "I did not laugh"; but [God] said, "Ah, but you did laugh!"

In Torah study, we often discuss Sarah's laughter upon learning she and Abraham will have a son and how the word for her laughter (ותצחק va-titzchak) is related to that son's name (יצחק yitzchak, Isaac). I don't recall it being mentioned, at least not often, that Abraham laughed first.

Gen. 17:17] Abraham fell flat on his face and laughed, thinking: "Can a child be born to a man of 100? Can 90-year-old Sarah bear a child?"

It seems to me too that there is something discussion-worthy in contrasting Sarah's inward laughter with Abraham's falling on his face laughing, but I'm not sure what that is at the moment.