Genesis 21:7

מי מלל לאברהם The word מי is used as an exclamation of praise alluding to the distinguished position of the Being spoken of. The sense therefore is: See, Who it is, and to what extent He keeps his promise! The Holy One, blessed be He, promises and performs! מלל SAID — Scripture employs here an unusual expression and does not use דבר, said, because its numerical value (i. e. of מלל) is one hundred, signifying as much as: Who was it who spoke in reference to the end of one hundred years of Abraham’s life (Genesis Rabbah 53:9). הניקה בנים שרה THAT SARAH WILL HAVE SUCKLED CHILDREN. What is the force of the word “children”, in the plural? On the feast-day princesses brought their children with them and she (Sarah) gave them suck, for these women said, “Sarah has not given birth to a son; she has brought into her house a foundling from the street” (Bava Metzia 87a).

וַתֹּ֗אמֶר מִ֤י מִלֵּל֙ לְאַבְרָהָ֔ם הֵינִ֥יקָה בָנִ֖ים שָׂרָ֑ה כִּֽי־יָלַ֥דְתִּי בֵ֖ן לִזְקֻנָֽיו׃

And she said, Who would have said to Avraham, that Sara should give children suck? for I have born him a son in his old age.