Leviticus 23:39-41

39"On the fifteenth day of the seventh month, when you have gathered in the produce of the land, you shall celebrate the feast of the Lord seven days. On the first day shall be a solemn rest, and on the eighth day shall be a solemn rest.

40And you shall take on the first day the fruit of splendid trees, branches of palm trees and boughs of leafy trees and willows of the brook, and you shall rejoice before the Lord your God seven days.

41You shall celebrate it as a feast to the Lord for seven days in the year. It is a statute forever throughout your generations; you shall celebrate it in the seventh month.