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.

Numbers 9:11

9:11 They may observe it on the fourteenth day of the second month at twilight; they are to eat it with bread made without yeast and with bitter herbs.