Leviticus 23:39-41

39“‘On the fifteenth day of the seventh month, when you gather in the produce of the land, you must celebrate a pilgrim festival of the Lord for seven days. On the first day is a complete rest and on the eighth day is complete rest.

40On the first day you must take for yourselves branches from majestic trees – palm branches, branches of leafy trees, and willows of the brook – and you must rejoice before the Lord your God for seven days.

41You must celebrate it as a pilgrim festival to the Lord for seven days in the year. This is a perpetual statute throughout your generations; you must celebrate it in the seventh month.