Exactly three months after the people of Israel left Egypt, they came to the Desert of Sinai.
References for Exodus 19:1
After they started out from Rephidim, they entered the Desert of Sinai. They camped there in the desert in front of the mountain.
Then Moses went up to God. The LORD called out to him from the mountain. He said, "Here is what I want you to say to my people, who came from Jacob's family. Tell the Israelites,
'You have seen for yourselves what I did to Egypt. You saw how I carried you on the wings of eagles and brought you to myself.
" 'Now obey me completely. Keep my covenant. If you do, then out of all of the nations you will be my special treasure. The whole earth is mine.
But you will be a kingdom of priests to serve me. You will be my holy nation.' That is what you must tell the Israelites."