Deuteronomy 16 - 17

1 “Observe the month of Abib, and keep the Passover to the Lord your God, for in the month of Abib the Lord your God brought you out of Egypt by night. 2 Therefore you shall sacrifice the Passover to the Lord your God, from the flock and the herd, in the place where the Lord chooses to put His name. 3 You shall eat no leavened bread with it; seven days you shall eat unleavened bread with it, that is, the bread of affliction (for you came out of the land of Egypt in haste), that you may remember the day in which you came out of the land of Egypt all the days of your life. 4 And no leaven shall be seen among you in all your territory for seven days, nor shall any of the meat which you sacrifice the first day at twilight remain overnight until morning …
— DEUTERONOMY 16 - 17