Thematic Bible: Passover first commemorated

The Lord spoke to Moses in the wilderness of Sinai, in the first month of the second year after they had come out of the land of Egypt: "The Israelites are to observe the Passover at its appointed time. In the fourteenth day of this month, at twilight, you are to observe it at its appointed time; you must keep it in accordance with all its statutes and all its customs." read more.
So Moses instructed the Israelites to observe the Passover. And they observed the Passover on the fourteenth day of the first month at twilight in the wilderness of Sinai; in accordance with all that the Lord had commanded Moses, so the Israelites did.