Exodus 19:14-16

Young's Literal Translation

¹⁴ And Moses cometh down from the mount unto the people, and sanctifieth the people, and they wash their garments;

¹⁵ and he saith unto the people, `Be ye prepared for the third day, come not nigh unto a woman.'

¹⁶ And it cometh to pass, on the third day, while it is morning, that there are voices, and lightnings, and a heavy cloud, on the mount, and the sound of a trumpet very strong; and all the people who [are] in the camp do tremble.