Numbers 9:4

And Moses spake unto the children of Israel, that they should keep the passover. The time now drawing nigh for the observation of it, it being now almost a year since their coming out of Egypt.

And…

Passover at Sinai. This, as being kept in the first month, was prior in time to the numbering of Num 1:1 ff, and to the other events narrated in this book. It is, however, recorded here as…

Here we have,

I. An order given for the solemnization of the passover, the day twelvemonth after they came out of Egypt, on the fourteenth day of the first month of the second year, some days before…