Parashas Vayikra · Aliyah 7 · Passuk 5
Chabad.org — English translation + Rashi
Torah Temima points to Yoma 36a / Toras Kohanim on vidui with chatat.
E-Daf / Tsurras Hadaf
PDF of the daf / source
English: When he becomes guilty in any of these, he shall confess that in which he has sinned.
Vidui as a prerequisite of kapparah — verbal confession accompanies the korban.
For each of the cases in this section (witness, tumah, oath), the sinner must confess the specific sin before (or as part of) bringing the offering. Confession is not optional.