Vayikra 16:29-31

Orthodox Jewish Bible

²⁹ And this shall be a chukkat olam (eternal decree) unto you: that in the Chodesh HaShevi’i, on the tenth day of the chodesh, ye shall afflict your nefashot, and do no melachah at all, whether it be ezrach (native) or the ger that sojourneth among you:

³⁰ For on that day shall the kohen make kapporah for you, to make you tahor, that ye may be tahor from all your chattot before Hashem.

³¹ It shall be a Shabbat Shabbaton unto you, and ye shall afflict your nefashot, by a chukkat olam.