Numbers 9:2-5

2“Let the children 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 rites and ceremonies you shall keep it.”

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

5And they kept the Passover on the fourteenth day of the first month, at twilight, in the Wilderness of Sinai; according to all that the Lord commanded Moses, so the children of Israel did.