'Keep the Passover' in the Bible
“The sons of Israel are to keep the Passover at its appointed time.
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.
“Say to the Israelites, ‘If any one of you or of your descendants becomes [ceremonially] unclean because of [touching] a dead body or is on a distant journey, he may, however, observe the Passover to the Lord.
But the man who is [ceremonially] clean and is not on a journey, and yet does not observe the Passover, that person shall be cut off from among his people [excluding him from the atonement made for them] because he did not bring the Lord’s offering at its appointed time; that man will bear [the penalty of] his sin.
If a stranger lives among you as a resident alien and observes the Passover to the Lord, in accordance with its statutes and its ordinances, so shall he do; you shall have one statute, both for the resident alien and for the native of the land.’”