Numbers 9:2-7

“The sons of Israel are to keep the Passover at its appointed time. On the fourteenth day of this month at twilight, you shall keep it at its appointed time; according to all its statutes and ordinances you shall keep it.” So Moses told the Israelites to observe the Passover. 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. But there were certain men who were [ceremonially] unclean because of [touching] the dead body of a man, so they could not observe the Passover on that day; so they came before Moses and Aaron that same day. Those men said to Moses, “We are [ceremonially] unclean because of [touching] a dead body. Why are we being restrained from presenting the LORD’S offering at its appointed time among the Israelites?”