Leviticus 23:39-40

39“ ‘So beginning with the fifteenth day of the seventh month, after you have gathered the crops of the land, celebrate the festival to the Lord for seven days; the first day is a day of sabbath rest, and the eighth day also is a day of sabbath rest.

40On the first day you are to take branches from luxuriant trees—from palms, willows and other leafy trees—and rejoice before the Lord your God for seven days.