Rashi on Numbers 28:18/רש"י על במדבר כ״ח:י״ח

1כל מלאכת עבדה [YE SHALL DO] NO SERVILE WORK — even work that is a necessity for you, as, for instance, a matter that may become lost (that cannot be postponed without irretrievable loss) and which is permissible on the intermediate days of Passover and Tabernacles (lit., the week days of the Festival) is forbidden on the Festival itself (see Rashi on Leviticus 23:8).