Numbers 9:8

5 And they kept the passover on the fourteenth day of the first month at even in the wilderness of Sinai: according to all that the LORD commanded Moses, so did the children of Israel.

6 And there were certain men, who were defiled by the dead body of a man, that they could not keep the passover on that day: and they came before Moses and before Aaron on that day:

7 And those men said unto him, We are defiled by the dead body of a man: wherefore are we kept back, that we may not offer an offering of the LORD in his appointed season among the children of Israel?

8 And Moses said unto them, Stand still, and I will hear what the LORD will command concerning you.

9 And the LORD spake unto Moses, saying,

10 Speak unto the children of Israel, saying, If any man of you or of your posterity shall be unclean by reason of a dead body, or be in a journey afar off, yet he shall keep the passover unto the LORD.

11 The fourteenth day of the second month at even they shall keep it, and eat it with unleavened bread and bitter herbs.