Deuteronomy 16:1-9

“Observe the month of Abib and celebrate the Passover to the LORD your God, for in the month of Abib the LORD your God brought you out of Egypt by night. You shall sacrifice the Passover [lamb] to the LORD your God from the flock or the herd, in the place where the LORD chooses to establish His Name (Presence). You shall not eat leavened bread with it; instead, for seven days you shall eat the Passover with unleavened bread, the bread of affliction (for you left the land of Egypt in haste); [do this] so that all the days of your life you may remember [thoughtfully] the day when you came out of the land of Egypt. For seven days no leaven shall be seen with you in all your territory, and none of the meat which you sacrificed the evening of the first day shall remain overnight until morning. You are not allowed to sacrifice the Passover [lamb] in any of your cities which the LORD your God is giving you; but at the place where the LORD your God chooses to establish His Name (Presence), you shall sacrifice the Passover [lamb] in the evening at sunset, at the time that you came out of Egypt. You shall cook and eat it in the place which the LORD your God chooses. In the morning you are to return to your tents. For six days you shall eat unleavened bread, and on the seventh day there shall be a celebration to the LORD your God; so you shall do no work [on that day]. “You shall count seven weeks for yourself; you shall begin to count seven weeks from the time you first put the sickle to the standing grain.