Numbers 28:18

18 On the first day hold a sacred assembly and do no regular work.

Read Numbers 28:18 Using Other Translations

In the first day shall be an holy convocation; ye shall do no manner of servile work therein:
On the first day there shall be a holy convocation. You shall not do any ordinary work,
The first day of the festival will be an official day for holy assembly, and no ordinary work may be done on that day.