Deuteronomy 16:8-10 World English Bible (WEB)
8 Six days you shall eat unleavened bread. On the seventh day shall be a solemn assembly to Yahweh your God. You shall do no work.
9 You shall count for yourselves seven weeks. From the time you begin to put the sickle to the standing grain you shall begin to count seven weeks. 10 You shall keep the feast of weeks to Yahweh your God with a tribute of a free will offering of your hand, which you shall give according to how Yahweh your God blesses you.