Leviticus 6:10

לא תאפה חמץ חלקם IT SHALL NOT BE BAKEN AS ANYTHING LEAVENED FOR THEIR PORTION — The remains of the meal-offering which become the portion of the priests, are also forbidden to be baked in the form of leavened (Menachot 55a). כחטאת וכאשם [IT IS MOST HOLY] AS THE SIN OFFERING OR THE GUILT OFFERING — the meal-offering of the sinner (v. 11) is as the sin-offering, therefore if he (the priest) takes the fistful out of it not as such (not having in mind that offering) it is invalid as is the sin-offering under such circumstances (cf. Rashi on 5:12); a free-will meal-offering (i.e. any of the other meal-offerings mentioned in ויקרא), however, is as the guilt-offering, therefore if he takes the fistful out of it not doing it as such, it is still valid (Sifra, Tzav, Chapter 3 3; Zevachim 11a).

לֹ֤א תֵאָפֶה֙ חָמֵ֔ץ חֶלְקָ֛ם נָתַ֥תִּי אֹתָ֖הּ מֵאִשָּׁ֑י קֹ֤דֶשׁ קׇֽדָשִׁים֙ הִ֔וא כַּחַטָּ֖את וְכָאָשָֽׁם׃

It shall not be baked with leaven. I have given it to them for their portion of my offerings made by fire; it is most holy, as is the sin offering, and the guilt offering.