Exodus 19:10-12, 14

And the LORD said unto Moses, Go unto the people, and sanctify them to day and to morrow, and let them wash their clothes, 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. And thou shalt set bounds unto the people round about, saying, Take heed to yourselves, that ye go not up into the mount, or touch the border of it: whosoever toucheth the mount shall be surely put to death

And Moses went down from the mount unto the people, and sanctified the people; and they washed their clothes.