Numbers 9:2-7

2“Have the Israelites celebrate the Passover at the appointed time. 3Celebrate it at the appointed time, at twilight on the fourteenth day of this month, in accordance with all its rules and regulations.” 4So Moses told the Israelites to celebrate the Passover, 5and 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. 6But 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 7and 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?”