Exodus 19:10-12, 14

The LORD said to Moses, “Go to the people and have them spend today and tomorrow preparing themselves. They must wash their clothes and be ready by the day after tomorrow. On that day I, the LORD, will come down on Mount Sinai, and all the people will see me. But you must set a limit around the mountain that the people are not to cross. Tell them not to go up on the mountain and not to touch the foot of it. Anyone who touches the mountain must be put to death

After Moses went down from the mountain to the people, he made them prepare themselves for service to God, and they washed their clothes.