Exodus 19:10-12, 14

Then the LORD told Moses, “Go down and prepare the people for my arrival. Consecrate them today and tomorrow, and have them wash their clothing. Be sure they are ready on the third day, for on that day the LORD will come down on Mount Sinai as all the people watch. Mark off a boundary all around the mountain. Warn the people, ‘Be careful! Do not go up on the mountain or even touch its boundaries. Anyone who touches the mountain will certainly be put to death.

So Moses went down to the people. He consecrated them for worship, and they washed their clothes.