Deuteronomy 16:9-12

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. 12Remember that you were slaves in Egypt, and follow carefully these decrees.