In Deuteronomy 16 we find the words:
“Observe the month Aviv and keep the Passover to the Lord your God, for in that month he brought you out of Egypt by night. You must sacrifice the Passover animal from the flock or the herd to the Lord your God in the place where he chooses to locate his name. You must not eat any yeast with it; for seven days you must eat with it (the English omits this while the Aleppo, Samaritan, and the dead sea scrolls have the words “with it”) unleavened bread, bread of affliction, for you came out of Egypt hurriedly. You must do this so you will remember for the rest of your life the day you came out of the land of Egypt. There must not be a scrap of yeast within your land for seven days, nor can any of the meat you sacrifice on the evening of the first day remain until the next morning. You may not sacrifice the Passover in just any of your villages that the Lord your God is giving you.” Deut 16:1-5
