In the third month after leaving Egypt, the Israelites come to the Wilderness of Sinai and camp in front of the mountain.
Exodus 19:1-2 (KJV)
In the third month, when the children of Israel were gone forth out of the land of Egypt, the same day came they into the wilderness of Sinai... and had pitched in the wilderness; and there Israel camped before the mount.
Exodus 19:1-2 (NIV)
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.