Numbers 9:2-7

“Have the Israelites celebrate the Passover at the appointed time. Celebrate it at the appointed time, at twilight on the fourteenth day of this month, in accordance with all its rules and regulations.” So Moses told the Israelites to celebrate the Passover, and they did so 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. But some of them could not celebrate the Passover on that day because they were ceremonially unclean on account of a dead body. So they came to Moses and Aaron that same day and said to Moses, “We have become unclean because of a dead body, but why should we be kept from presenting the LORD’s offering with the other Israelites at the appointed time?”