So Moses told the children of Israel that they should keep the Passover.
Numbers 9:4
Surrounding context
9:3 On 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."
9:4 So Moses told the children of Israel that they should keep the Passover.
9:5 And 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.