Mishnayos Kerisos Perek 3 Mishnah 1

If witnesses said to a person: We saw that you ate forbidden fat, he is liable to bring a sin offering if he did so unwittingly. If a witness says: He ate forbidden fat, and a witness says: He did not eat forbidden fat, or if a woman says: He ate forbidden fat, and a woman says: He did not eat forbidden fat, he is liable to bring a provisional guilt offering, brought by one who is uncertain as to whether he committed a sin that requires a sin offering. If a witness says: He ate forbidden fat, and the person himself says: I did not eat forbidden fat, he is exempt. If two witnesses say: He ate forbidden fat, and the person himself says: I did not eat forbidden fat, Rabbi Meir deems him liable to bring a sin offering. Rabbi Meir said: This conclusion can be derived a fortiori: If two witnesses could have brought him liability to receive the severe punishment of death, can they not bring him liability to sacrifice an offering, which is relatively lenient? The Rabbis said to him: Witnesses are unable to render another person liable to bring an offering contrary to his statement, as what if he wishes to say: I did so intentionally, in which case he would be exempt from bringing an offering?

אָמְרוּ לוֹ אָכַלְתָּ חֵלֶב, מֵבִיא חַטָּאת. עֵד אוֹמֵר אָכַל וְעֵד אוֹמֵר לֹא אָכַל, אִשָּׁה אוֹמֶרֶת אָכַל וְאִשָּׁה אוֹמֶרֶת לֹא אָכַל, מֵבִיא אָשָׁם תָּלוּי. עֵד אוֹמֵר אָכַל וְהוּא אוֹמֵר לֹא אָכַלְתִּי, פָּטוּר. שְׁנַיִם אוֹמְרִים אָכַל וְהוּא אוֹמֵר לֹא אָכַלְתִּי, רַבִּי מֵאִיר מְחַיֵּב. אָמַר רַבִּי מֵאִיר, אִם הֱבִיאוּהוּ שְׁנַיִם לְמִיתָה חֲמוּרָה, לֹא יְבִיאוּהוּ לְקָרְבָּן הַקַּל. אָמְרוּ לוֹ, מָה אִם יִרְצֶה לוֹמַר מֵזִיד הָיִיתִי: