Numbers 9:2-5

Moreover let the children of Israel keep the passover in its appointed season. In the fourteenth day of this month, at even, ye shall keep it in its appointed season: according to all the statutes of it, and according to all the ordinances thereof, shall ye keep it. And Moses spake unto the children of Israel, that they should keep the passover. And they kept the passover in the first month, on the fourteenth day of the month, at even, in the wilderness of Sinai: according to all that Jehovah commanded Moses, so did the children of Israel.