Deuteronomy 16:10

16:10 Then you are to celebrate the Festival of Weeks before the Lord your God with the voluntary offering that you will bring, in proportion to how he has blessed you.

Deuteronomy 16:15

16:15 You are to celebrate the festival seven days before the Lord your God in the place he chooses, for he will bless you in all your productivity and in whatever you do; so you will indeed rejoice!