Exodus 19:11

American Standard Version

and be ready against the third day; for the third day Jehovah will come down in the sight of all the people upon mount Sinai.

Exodus 19:11 in other translations

and be ready for the third day; for on the third day Yahweh will come down in the sight of all the people on Mount Sinai.

9And Jehovah said unto Moses, Lo, I come unto thee in a thick cloud, that the people may hear when I speak with thee, and may also believe thee for ever. And Moses told the words of the people unto Jehovah.
10And Jehovah said unto Moses, Go unto the people, and sanctify them to-day and to-morrow, and let them wash their garments,
11and be ready against the third day; for the third day Jehovah will come down in the sight of all the people upon mount Sinai.
12And thou shalt set bounds unto the people round about, saying, Take heed to yourselves, that ye go not up into the mount, or touch the border of it: whosoever toucheth the mount shall be surely put to death:
13no hand shall touch him, but he shall surely be stoned, or shot through; whether it be beast or man, he shall not live: when the trumpet soundeth long, they shall come up to the mount.