Leviticus 23:41-43

41You must observe this festival to the Lord for seven days every year. This is a permanent law for you, and it must be observed in the appointed month from generation to generation.

42For seven days you must live outside in little shelters. All native-born Israelites must live in shelters.

43This will remind each new generation of Israelites that I made their ancestors live in shelters when I rescued them from the land of Egypt. I am the Lord your God.”