Shemot 19:10-11

Orthodox Jewish Bible

¹⁰ So Hashem said unto Moshe, Go unto HaAm, and set them apart as kodesh today and tomorrow, and let them wash their clothing,

¹¹ And be ready by Yom HaShelishi; for Yom HaShelishi Hashem will come down in the sight of kol HaAm upon Mt. Sinai.