Numbers 9:6-11

6And 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:

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

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

9And the LORD spoke to Moses, saying,

10Speak to 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 to the LORD.

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