Exodus 12:1

And the Lord spake unto Moses and Aaron in the land of Egypt, saying,

Cross-reference

Exodus 40:2 Historical context

Exodus 40:2 shows the tabernacle set up on the first day of the first month, using the calendar established here.

Numbers 9:2 Parallel

Numbers 9:2 commands the Israelites to celebrate Passover at its appointed time, directly referencing this original institution.

Ezekiel 45:21 commands Passover in the first month on the 14th day, echoing the law given here.