Deuteronomy 16:2-4 New Revised Standard Version (NRSV)
2 You shall offer the passover sacrifice to the Lord your God, from the flock and the herd, at the place that the Lord will choose as a dwelling for his name. 3 You must not eat with it anything leavened. For seven days you shall eat unleavened bread with it—the bread of affliction—because you came out of the land of Egypt in great haste, so that all the days of your life you may remember the day of your departure from the land of Egypt. 4 No leaven shall be seen with you in all your territory for seven days; and none of the meat of what you slaughter on the evening of the first day shall remain until morning.