Numbers 9:1-4

1The Lord spoke to Moses in the wilderness of Sinai, in the first month of the second year after they had come out of the land of Egypt:

2“The Israelites are to observe the Passover at its appointed time.

3In 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.”

4So Moses instructed the Israelites to observe the Passover.