Rashi on Genesis 21:21/רש"י על בראשית כ״א:כ״א

1מארץ מצרים FROM THE LAND OF EGYPT — from the place where she was brought up — as it is said (16:1) “And she (Sarah) had an Egyptian handmaid [whose name was Hagar]”. That is what the popular proverb says: “Throw a stick into the air and it will fall back to (literally, stand on) its element” (Genesis Rabbah 53:15).