In the fifth aliyah G-d says to Moshe to tell the people to sanctify themselves. They should immerse in the mikvah, and husbands and wives are to separate for three days. They should set bounds around about Mt. Sinai, and no man or beast should go past the bounds.
On the third day (the sixth of Sivan), in the morning, there is thundering and lightning and a thick cloud. The sound of an exceedingly loud shofar is heard. Mt. Sinai is seen smoking and shaking, and the shofar grows louder and louder.