Deuteronomy 16:7

No yeast shall be seen with you in all your borders seven days; neither shall any of the meat, which you sacrifice the first day at evening, remain all night until the morning.

You may not sacrifice the Passover within any of your gates which the LORD your God gives you;

but at the place which the LORD your God shall choose to cause his name to dwell in, there you shall sacrifice the Passover at evening, at the going down of the sun, at the season that you came out of Egypt.

Six days you shall eat unleavened bread. On the seventh day shall be a solemn assembly to the LORD your God. You shall do no work.

You shall count for yourselves seven weeks. From the time you begin to put the sickle to the standing grain you shall begin to count seven weeks.

You shall keep the feast of weeks to the LORD your God with a tribute of a free will offering of your hand, which you shall give according to how the LORD your God blesses you.