Numbers 9:1, 5, 11

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

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.

In the second month on the fourteenth day at twilight they shall keep it. They shall eat it with unleavened bread and bitter herbs.