Halakhah do Kapłańska 23:35

The commandment of resting on the first day of the holiday of Sukkot: To rest from any work which is not for the needs of food for the soul on the first day of the holiday of Sukkot, as it is stated (Leviticus 23:35), "On the first day, a holy occasion."

He prohibited doing work on the first day of the Holiday (Sukkot). And that is His saying, "you shall not do any work of labor" (Leviticus 23:35). (See Parashat Emor; Mishneh Torah, Rest on a Holiday 1.)