"You shall count seven weeks for yourself; begin to count the seven weeks from the time you begin to put the sickle to the grain.
Deuteronomy 16:9
Surrounding context
16:8 Six days you shall eat unleavened bread, and on the seventh day there shall be a sacred assembly to the LORD your God. You shall do no work on it.
16:9 "You shall count seven weeks for yourself; begin to count the seven weeks from the time you begin to put the sickle to the grain.
16:10 Then you shall keep the Feast of Weeks to the LORD your God with the tribute of a freewill offering from your hand, which you shall give as the LORD your God blesses you.