Exodus 19:9 KJV

7And Moses came and called for the elders of the people, and laid before their faces all these words which the LORD commanded him.

8And all the people answered together, and said, All that the LORD hath spoken we will do. And Moses returned the words of the people unto the LORD.

9And 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.

10And the LORD said unto Moses, Go unto the people, and sanctify them to day and to morrow, and let them wash their clothes,

11And 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.