Leviticus 16:29-31

“This is standard practice for you, a perpetual ordinance. On the tenth day of the seventh month, both the citizen and the foreigner living with you are to enter into a solemn fast and refrain from all work, because on this day atonement will be made for you, to cleanse you. In the presence of GOD you will be made clean of all your sins. It is a Sabbath of all Sabbaths. You must fast. It is a perpetual ordinance.