Leviticus 23:10, 11
"Speak to the Israelites and say, 'When you enter the land I am giving you and reap its harvest, you are to bring to the priest the sheaf of the firstfruits of your harvest. . . .

Leviticus 25:8
And you shall count off seven sabbaths of years--seven times seven years--so that time of the seven sabbatical years amounts to forty-nine years.

Exodus 34:22
And you are to celebrate the Feast of Weeks with the firstfruits of the wheat harvest, and the Feast of Ingathering at the turn of the year.

Deuteronomy 16:9, 10
You are to count off seven weeks from the time you first put the sickle to the standing grain. . . .