Leviticus 6:10 "It shall not be baked with leaven. I have given it to them for their portion of My offerings made by fire"

This Negative Mitzvah refers to the portion of the meal-offering that is given to the priests to eat.

The priest scoops up part of the mixture (in a special way) and offers it on the altar. The remainder is eaten by the priests themselves. This portion may not be baked as leavened bread (Chametz).