Exodus 19:9-11

Darby Translation

⁹ And Jehovah said to Moses, Lo, I will come to thee in the cloud's thick darkness, that the people may hear when I speak with thee, and believe thee also for ever. And Moses told the words of the people to Jehovah.

¹⁰ And Jehovah said to Moses, Go to the people, and hallow them to-day and to-morrow, and let them wash their clothes;

¹¹ and let them be ready for the third day; for on the third day Jehovah will come down before the eyes of all the people on mount Sinai.