Deuteronomy 16:9-11

9Count off seven weeks from the time you begin to put the sickle to the standing grain.

10Then celebrate the Festival of Weeks to the Lord your God by giving a freewill offering in proportion to the blessings the Lord your God has given you.

11And rejoice before the Lord your God at the place he will choose as a dwelling for his Name—you, your sons and daughters, your male and female servants, the Levites in your towns, and the foreigners, the fatherless and the widows living among you.