Exodus 19:16-25 NIV
On the morning of the third day there was thunder and lightning, with a thick cloud over the mountain, and a very loud trumpet blast. Everyone in the camp trembled. Then Moses led the people out of the camp to meet with God, and they stood at the foot of the mountain. Mount Sinai was covered with smoke, because the LORD descended on it in fire. The smoke billowed up from it like smoke from a furnace, and the whole mountain trembled violently. As the sound of the trumpet grew louder and louder, Moses spoke and the voice of God answered him.
The LORD descended to the top of Mount Sinai and called Moses to the top of the mountain. So Moses went up and the LORD said to him, “Go down and warn the people so they do not force their way through to see the LORD and many of them perish. Even the priests, who approach the LORD, must consecrate themselves, or the LORD will break out against them.”
Moses said to the LORD, “The people cannot come up Mount Sinai, because you yourself warned us, ‘Put limits around the mountain and set it apart as holy.’ ”
The LORD replied, “Go down and bring Aaron up with you. But the priests and the people must not force their way through to come up to the LORD, or he will break out against them.”
So Moses went down to the people and told them.
NIV: New International Version