Numbers 9:6

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:

There were certain men ... defiled by the dead. To discharge the last offices to the remains of deceased relatives was imperative; and yet attendance on a funeral entailed ceremonial defilement, which led to exclusion from all society and from the camp for seven days (Numbers 5:2). Some persons who were in this situation at the arrival of the first paschal anniversary, being painfully perplexed about the course of duty, because they were temporarily disqualified at the proper season, and having no opportunity of supplying their want, were liable to a total privation of all their privileges, laid their case before Moses. Jewish writers assert that these men were the persons who had carried out the dead bodies of Nadab and Abihu (see Blunt's 'Coincidences,' p. 94).