Exodus 12:42
This is a night to be observed to the LORD, because he brought them out of the land of Egypt. This is a night of the LORD, to be kept of all the children of Israel and of their generations after them.
Deuteronomy 16:1-6
Observe the month of Abib, and offer Passover unto the LORD thy God. For in the month of Abib, the LORD thy God brought thee out of Egypt by night:
Exodus 12:14
And this day shall be unto you a remembrance, and ye shall keep it holy unto the LORD: even throughout your generations after you shall ye keep it holy day, that it be a custom forever.
Exodus 13:10
see thou keep therefore this ordinance in his season from year to year.