Numbers 9:2-5

2"Let the people of Israel keep the Passover at its appointed time.

3On 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."

4So Moses told the people of Israel that they should keep the Passover.

5And 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.