The Passover is first mentioned in Exodus 12. It is described as a ritual that Moses and the Hebrew people were to observe in order to be saved from the Angel of Death. In Exodus 12, the Lord instructs Moses and Aaron to select a lamb and make preparations for a feast. They were also to put its blood on their doorposts, so that when the Lord passes over the house, He would spare the Hebrews from being killed.
In Exodus 12:43-45, it mentions the commandment to keep the feast of the Passover in future generations.
In Numbers 9, there’s a retelling of this commandment, and the Lord tells Moses, Aaron and the people once again to keep the Passover ordinance.
In Deuteronomy 16, the Lord commands the Israelites to observe the Passover once again. He also explains the meaning of the feast, which is to remember the Hebrew’s deliverance from Egypt.
We see the Passover celebrated numerous times throughout the books of Exodus, Leviticus, Numbers, Deuteronomy, Joshua, 2 Kings, 2 Chronicles and Ezra. In the New Testament, Jesus and his disciples also celebrate the Passover (see Luke 22:14–20).
You can read the chapters of the Bible in full online at the Bible Gateway (https://www.biblegateway.com/).