Parashas Metzora · Passuk 14:20
Chabad.org — English translation + Rashi
Torah Temima points to Pesachim 59b (verified on the daf).
E-Daf.com — Tsurras Hadaf (size=3)
HebrewBooks / Shas PDF of the daf
English: “And the kohen shall offer up the olah” — the olah that he has already offered up; from here we learn that if he offered the olah before the chatas it is still valid.
Order of offerings
Chazal teach that although the preferred order is chatas before olah, if the olah was offered first it remains valid.