Leviticus 23:39-40

39‘On exactly the fifteenth day of the seventh month (nearly October), when you have gathered in the crops of the land, you shall celebrate the feast of the Lord for seven days, with a Sabbath rest on the first day and a Sabbath rest on the eighth day.

40Now on the first day you shall take for yourselves the foliage of beautiful trees, branches of palm trees, and boughs of thick (leafy) trees, and willows of the brook [and make booths of them]; and you shall rejoice before the Lord your God for seven days.