Parashas Metzora · Passuk 14:32
Chabad.org — English translation + Rashi
Torah Temima points to Kerisus 28a (verified on the daf).
E-Daf.com — Tsurras Hadaf (size=3)
HebrewBooks / Shas PDF of the daf
English: “This is the Toras” — “Toras” includes a poor metzora who brought the rich man’s offering, that he has fulfilled his obligation; one might think that even a rich man who brought the poor man’s offering has fulfilled it, therefore it says “this.”
One-directional substitution
Chazal teach that a poor metzora who brings the richer offering has fulfilled his duty, but a rich metzora who brings the poorer offering has not.