Numbers 9:1

Passover Regulations

9:1 The 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:

Numbers 9:5

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.