Leviticus 16:29-31

29“It is to be a statute to you forever, that in the seventh month, on the tenth day of the month, you are to afflict your souls, and do no kind of work—both the native-born and the outsider dwelling among you.

30For on this day atonement will be made for you, to cleanse you. From all your sins you will be clean before Adonai.

31It is a Shabbat of solemn rest to you, and you are to afflict your souls. It is a statute forever.