Exodus 19:9-11

American Standard Version

⁹ And Jehovah said unto Moses, Lo, I come unto thee in a thick cloud, that the people may hear when I speak with thee, and may also believe thee for ever. And Moses told the words of the people unto Jehovah. ¹⁰ And Jehovah said unto Moses, Go unto the people, and sanctify them to-day and to-morrow, and let them wash their garments, ¹¹ and be ready against the third day; for the third day Jehovah will come down in the sight of all the people upon mount Sinai.