Leviticus 23:39-41

Howbeit on the fifteenth day of the seventh month, when ye have gathered in the fruits of the land, ye shall keep the feast of Jehovah seven days: on the first day shall be a solemn rest, and on the eighth day shall be a solemn rest. 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. And ye shall keep it a feast unto Jehovah seven days in the year: it is a statute for ever throughout your generations; ye shall keep it in the seventh month.