Numbers 9:2-3

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.”

Numbers 9:7

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?”

Numbers 9:13

9:13 But the man who is ceremonially clean, and was not on a journey, and fails to keep the Passover, that person must be cut off from his people. Because he did not bring the Lord’s offering at its appointed time, that man must bear his sin.