Chabad.org — English translation + Rashi
Torah Temimah points to Toras Kohanim (Sifra), Vayikra Dibbura DeNedavah, Chapter 5 (ha-olah — even shelo lishmah).
Sefaria — Sifra / Toras Kohanim, Dibbura DeNedavah, Chapter 5
English: I have only [the case of] one slaughtered for its own sake; from where [do we know] one not for its own sake? The verse says “the olah” — whatever is an olah requires stripping.
Ribbuy from “the olah” — any olah requires hafshatah, including shelo lishmah.
Hafshatah applies to any animal that is an olah, including one slaughtered shelo lishmah. “The olah” is the inclusive term that extends the duty beyond the ideal case.