Numbers 9:2-5

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.