Positive commandment · Mitzvat Aseh #165 of 613
To rest on [this] fast day
לשבות ביום הצום
The verse · Vayikra 16:31
שַׁבַּת שַׁבָּתוֹן הִיא לָכֶם וְעִנִּיתֶם אֶת־נַפְשֹׁתֵיכֶם חֻקַּת עוֹלָם
“It shall be a sabbath of solemn rest to you, and you shall afflict your souls, by a statute forever.”
The Rambam’s words
To rest on [this] fast day, as [Leviticus 16:31] states: "It shall be a Shabbat of Sabbaths...."
לשבות ביום הצום, שנאמר: "שבת שבתון" (ויקרא טז,לא; ויקרא כג,לב).
Why · Sefer HaChinuch #317
Resting from work on Yom Kippur
“It is from the roots of the commandment from the angle of the simple understanding [that it is] so that we not be preoccupied with anything, and [so] place all of our thoughts and all of our intent to request pardon and forgiveness from the Master of all on that day, which is prepared for the forgiveness of iniquities from the day that the world was created — and as I have written in Acharei Mot in the commandment of the service of Yom Kippur (Sefer HaChinukh 185).”
Who & when
“And it is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Rest on the Tenth of Tishrei הלכות שביתת עשור