Deuteronomy 16:10

10 Then 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.

Read Deuteronomy 16:10 Using Other Translations

And thou shalt keep the feast of weeks unto the LORD thy God with a tribute of a freewill offering of thine hand, which thou shalt give unto the LORD thy God, according as the LORD thy God hath blessed thee:
Then you shall keep the Feast of Weeks to the LORD your God with the tribute of a freewill offering from your hand, which you shall give as the LORD your God blesses you.
Then celebrate the Festival of Harvest to honor the LORD your God. Bring him a voluntary offering in proportion to the blessings you have received from him.