Exodus 19:10 in the World English Bible
The LORD said to Moses, “Go to the people, and sanctify them today and tomorrow, and let them wash their garments,
Context
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.