Numbers 9:3-7

³On the fourteenth day of this month, at twilight, you shall celebrate it at its appointed time; you shall celebrate it in accordance with all its statutes and all its ordinances.” ⁴So Moses told the sons of Israel to celebrate the Passover. ⁵And they celebrated the Passover in the first month, on the fourteenth day of the month, at twilight, in the wilderness of Sinai; in accordance with everything that the Lord had commanded Moses, so the sons of Israel did. ⁶But there were some men who were unclean because of contact with a dead person, so that they could not celebrate Passover on that day; and they came before Moses and Aaron on that day. ⁷Those men said to him, “Though we are unclean because of a dead person, why are we kept from presenting the offering of the Lord at its appointed time among the sons of Israel?”