Numbers 9:1, 5, 11

The LORD spoke to Moses in the Desert of Sinai in the first month of the second year after they came out of Egypt. He said

and they did so in the Desert of Sinai at twilight on the fourteenth day of the first month. The Israelites did everything just as the LORD commanded Moses.

but they are to do it on the fourteenth day of the second month at twilight. They are to eat the lamb, together with unleavened bread and bitter herbs.