Exodus 19:1-3

On the first day of the third month after the Israelites left Egypt—on that very day—they came to the Desert of Sinai. After they set out from Rephidim, they entered the Desert of Sinai, and Israel camped there in the desert in front of the mountain. Then Moses went up to God, and the LORD called to him from the mountain and said, “This is what you are to say to the descendants of Jacob and what you are to tell the people of Israel