Exodus 19:1-3

In the third month after the children of Israel were gone forth out of the land of Egypt, the same day came they into the wilderness of Sinai. And when they were departed from Rephidim, and were come to the wilderness of Sinai, they encamped in the wilderness; and there Israel encamped before the mount. And Moses went up unto God, and Jehovah called unto him out of the mountain, saying, Thus shalt thou say to the house of Jacob, and tell the children of Israel