Deuteronomy 16:8-10 Holman Christian Standard Bible (HCSB)
8 You must eat unleavened bread for six days. On the seventh day there is to be a solemn assembly to the Lord your God, and you must not do any work.
The Festival of Weeks
9 “You are to count seven weeks, counting the weeks from the time the sickle is first put to the standing grain. 10 You are to celebrate the Festival of Weeks to the Lord your God with a freewill offering that you give in proportion to how the Lord your God has blessed you.