Deuteronomy 16:9-10

The Festival of Weeks

16:9 You must count seven weeks; you must begin to count them from the time you begin to harvest the standing grain. 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 16:16

16:16 Three times a year all your males must appear before the Lord your God in the place he chooses for the Festival of Unleavened Bread, the Festival of Weeks, and the Festival of Temporary Shelters; and they must not appear before him empty-handed.