Parashas Acharei Mos · Passuk 16:29
Chabad.org — English translation + Rashi
Torah Temima points to Yoma 74b.
English: “You shall afflict your souls” — might one sit in the sun or cold to cause suffering? The adjacent prohibition of melachah teaches that affliction, like melachah, is a matter of refraining (shev ve’al ta’aseh).
Hekesh to melachah (shev ve’al ta’aseh)
Innui on Yom Kippur is fulfilled by abstaining from the five afflictions, not by actively seeking physical discomfort.