Exodus 19:9-11

Authorized (King James) Version

⁹ And the Lord said unto Moses, Lo, I come unto thee in a thick cloud, that the people may hear when I speak with thee, and believe thee for ever. And Moses told the words of the people unto the Lord.

¹⁰ And the Lord said unto Moses, Go unto the people, and sanctify them to day and to morrow, and let them wash their clothes, ¹¹ and be ready against the third day: for the third day the Lord will come down in the sight of all the people upon mount Sinai.