Rashi on Leviticus 23:31/רש"י על ויקרא כ״ג:ל״א

1'‎‎כל מלאכה וגו‎ [YE SHALL NOT DO] ANY WORK — This is repeated (cf v. 30) in order to make one who does work on Yom Kippur transgress several negative commands. Or, it is repeated, in order to prohibit working in the night of Yom Kippur, just as well as working during the day itself (Yoma 81a).