הלכה על יומא 148:8

The commandment of the fast on the tenth day of Tishrei: To fast on the tenth day of Tishrei, and this is called The Day of Atonements (Yom HaKippurim), as it is stated (Leviticus 23:27), "But on the tenth of the month, etc. you shall afflict your souls." The explanation appears is Sifra, Achrei Mot, Chapter 7:3): "[This refers to] affliction that causes a diminishing of the soul. What is this? This is eating and drinking." And so [too,] did they, may their memory be blessed, explain in the Gemara (Yoma 74b). And the tradition also came about it, that it is forbidden for washing, anointing, wearing shoes, and sexual relations. And the language of Sifra, Parshat Achrei Mot, Chapter 8:3 is "From where [do we know] that Yom Kippur is forbidden for washing, anointing, [wearing shoes] and sexual relations? [Hence] we learn to say (Leviticus 23:32), 'A Shabbat of shabbaton'" - meaning that the doubling of Shabbat (rest) indicates resting from these things [as well as] resting from nourishment of the body.