Deuteronomy 16:3-4

3Thou shalt eat no leavened bread with it; seven days shalt thou eat unleavened bread with it, even the bread of affliction; for thou camest forth from the land of Egypt in haste: that thou mayest remember the day when thou camest forth from the land of Egypt all the days of thy life.

4And there shall be no leavened bread seen with thee in all thy land seven days; neither shall there any thing of the flesh, which thou didst sacrifice the first day at evening, remain all night until the morning.