Leviticus 16:29-31

It shall be a statute to you forever that in the seventh month [nearly October] on the tenth day of the month you shall afflict yourselves [by fasting with penitence and humiliation] and do no work at all, either the native-born or the stranger who dwells temporarily among you. For on this day atonement shall be made for you, to cleanse you; from all your sins you shall be clean before the Lord. [Heb. 10:1, 2; I John 1:7, 9.] It is a sabbath of [solemn] rest to you, and you shall afflict yourselves [by fasting with penitence and humiliation]; it is a statute forever.