Numbers 9:4-6

American Standard Version

⁴ And Moses spake unto the children of Israel, that they should keep the passover. ⁵ And they kept the passover in the first month, on the fourteenth day of the month, ^[a]at even, in the wilderness of Sinai: according to all that Jehovah commanded Moses, so did the children of Israel. ⁶ And there were certain men, who were unclean by reason of the dead body of a man, so that they could not keep the passover on that day: and they came before Moses and before Aaron on that day: