Numbers 9:2-5

“Tell the Israelites to celebrate the Passover at the appointed time. That appointed time is the fourteenth day of this month at twilight; they must obey all the rules about it.” So Moses told the Israelites to celebrate the Passover, and they did; it was in the Desert of Sinai at twilight on the fourteenth day of the first month. The Israelites did everything just as the LORD commanded Moses.