Midrasch zu Wajikra 23:43

11) And thus does Ezra say (Nechemiah 8:15) "and that they must announce and proclaim throughout all their cities and Jerusalem, saying: Go out to the mountains and bring olive leaves, and olive-tree leaves and hadas leaves, and date-palm leaves, and plaited-tree leaves to make succoth, as it is written" (Vayikra 23:43) "So that your generations know that I caused the children of Israel to dwell in succoth when I took them out of the land of Egypt." R. Eliezer says that they were booths, literally; R. Akiva says that they were clouds of glory. "when I took them out of the land of Egypt." We are hereby taught that even the succah is a reminder of the exodus from Egypt.