Numbers 9:2-7

ISV(i) 2 “The Israelis are to observe the Passover at its appointed time 3 on the fourteenth day of this month. You are to observe it at this appointed time between the evenings. You are to observe it according to all its decrees and laws.”
4 So Moses instructed the Israelis to observe the Passover. 5 They observed the Passover on the fourteenth day of the first month at twilight, in the Wilderness of Sinai. The Israelis did everything that the LORD had commanded through Moses.
6 Special Passover RulesBut there were men who couldn’t observe the Passover that day because they had come in contact with a corpse. That very day, they approached Moses and Aaron 7 and asked, “Why can’t we bring an offering to the LORD at the appointed time among the Israelis, even though we are unclean because we came in contact with a corpse?”