The Lord spoke to Moses in the tent of meeting in the Desert of Sinai. It was the first day of the second month in the second year after leaving Egypt. He said,
You will celebrate it on the fourteenth day of the second month at dusk. You must eat the Passover animal along with unleavened bread and bitter herbs.
and they celebrated it on the fourteenth day of the first month at dusk while they were in the Desert of Sinai. The Israelites did everything as the Lord had commanded Moses.