Leviticus 23:39-41

39On the fifteenth day of the seventh month, after you have gathered the produce of the land, you are to celebrate a feast to the LORD for seven days. There shall be complete rest on the first day and also on the eighth day.

40On the first day you are to gather the fruit of majestic trees, the branches of palm trees, and the boughs of leafy trees and of willows1 of the brook. And you are to rejoice before the LORD your God for seven days. 41You are to celebrate this as a feast to the LORD for seven days each year. This is a permanent statute for the generations to come; you are to celebrate it in the seventh month.