Sarah's Laughter and the Yod Given to Isaac in Midrash Aggadah

"And Sarah said, 'God has made laughter for me,' etc." (Genesis 21:6) — for at the time that Sarah conceived, all the barren women in the land conceived, and just as she rejoiced, so all the barren women rejoiced. Another interpretation: "He has made laughter for me" — merit caused Isaac to be born. This teaches that the Holy One, blessed be He, took from me a yod and raised up for me in place of the yod a heh, and that yod was given to Isaac.