Deuteronomy 16:9-11

9You are to count off seven weeks from the time you first put the sickle to the standing grain. 10And you shall celebrate the Feast of Weeks1 to the LORD your God with a freewill offering that you give in proportion to how the LORD your God has blessed you, 11and you shall rejoice before the LORD your God in the place He will choose as a dwelling for His Name—you, your sons and daughters, your menservants and maidservants, and the Levite within your gates, as well as the foreigner, the fatherless, and the widows among you.