Leviticus 23:34, 40

Speak unto the children of Israel, saying, On the fifteenth day of this seventh month is the feast of tabernacles for seven days unto Jehovah.

And ye shall take you on the first day the fruit of goodly trees, branches of palm-trees, and boughs of thick trees, and willows of the brook; and ye shall rejoice before Jehovah your God seven days.