ספֿרי מצוות אויף ויקרא 23:36

These six days on which Scripture prohibited labor—being the first and seventh days of Passover, the first and eighth days of Sukkot, the day of Shavuot and the first day of the seventh month (Rosh Hashanah)—are called holidays (yamim tovim). The [degree of] cessation of work is equal in all of them, in that all work is prohibited except for labor that is for the sake of eating—as it is stated (Exodus 12:16), "only anything that is eaten by any person."

And the eighth day of it.

To offer up an additional sacrifice on the Feast of Tabernacles, as it is said, “…. and ye shall offer a burnt-offering, a sacrifice made by fire of sweet savour” (Num. 29:12-34).