Numbers 9:1-5

And 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, saying, “Let the people of Israel keep the Passover at its appointed time. On the fourteenth day of this month, at twilight, you shall keep it at its appointed time; according to all its statutes and all its rules you shall keep it.” So Moses told the people 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 twilight, in the wilderness of Sinai; according to all that the LORD commanded Moses, so the people of Israel did.