Deuteronomy 16:9-12

9Seven weeks you are to count for yourself—from the time you begin to put the sickle to the standing grain you will begin to count seven weeks.

10Then you will keep the Feast of Shavuot to Adonai your God with a measure of a freewill offering from your hand, which you are to give according to how Adonai your God blesses you.

11So you will rejoice before Adonai your God in the place Adonai your God chooses to make His Name dwell—you, your son and daughter, slave and maid, Levite and outsider, orphan and widow in your midst.

12You will remember that you were a slave in Egypt, and you are to take care and do these statutes.