Parashas Acharei Mos · Passuk 16:31
Chabad.org — English translation + Rashi
Torah Temima points to Chullin 101b.
English: From where that one who unwittingly labored on a Yom Kippur that fell on Shabbos is liable separately for each? From “it is a sabbath of solemn rest” — it is Yom Kippur (distinct from Shabbos).
Separate liability Shabbos / Yom Kippur
When Yom Kippur coincides with Shabbos, melachah incurs independent liability for each sanctity.