Exodus 34:22
And you shall observe the feast of weeks, of the first fruits of wheat harvest, and the feast of ingathering at the year's end.
Torrey's Topical Textbook—AKJV

Deuteronomy 16:10
And you shall keep the feast of weeks to the LORD your God with a tribute of a freewill offering of your hand, which you shall give to the LORD your God, according as the LORD your God has blessed you:
Torrey's Topical Textbook—AKJV