Leviticus 23:41
Observe it as a pilgrimage festival in the presence of the LORD for seven days of the year. This is to be an eternal ordinance throughout your generations. Observe the festival during the seventh month.
Numbers 29:12
"You are to hold a sacred assembly on the fifteenth day of the same seventh month. No servile work is to be done. You are to celebrate a festival to the LORD for seven days by
Nehemiah 8:18
and Ezra continued to read from the Book of the Law of God day by day, from the first day through the last. They celebrated for seven days, and on the eighth day they held a solemn assembly according to regulation.