Numbers 9:2-7

9:2 “The Israelites are to observe the Passover at its appointed time. 9:3 In the fourteenth day of this month, at twilight, you are to observe it at its appointed time; you must keep it in accordance with all its statutes and all its customs.” 9:4 So Moses instructed the Israelites to observe the Passover. 9:5 And they observed the Passover on the fourteenth day of the first month at twilight in the wilderness of Sinai; in accordance with all that the Lord had commanded Moses, so the Israelites did.

9:6 It happened that some men who were ceremonially defiled by the dead body of a man could not keep the Passover on that day, so they came before Moses and before Aaron on that day. 9:7 And those men said to him, “We are ceremonially defiled by the dead body of a man; why are we kept back from offering the Lord’s offering at its appointed time among the Israelites?”