Lévitique 6:10

Their portion of the residue of the mincha of My oblations given to them shall not be baked with leaven; it is most sacred, as the sin offering and as the trespass offering.

It will not be allowed to leaven This is the core commandment of Passover.

as are the sin-offering and the guilt-offering so is the meal-offering.

I HAVE GIVEN IT AS THEIR PORTION OF MY OFFERINGS. Even to apportion it [i.e., the residue of the meal-offering which the priests are to eat] they are not permitted to do until after the parts given to the fire [i.e., the handful] have gone up on the altar. It is from here that we learn that the same law applies to all hallowed offerings, as it is written, I have given it as their portion of My offerings; it is most holy.
It shall not be baked as anything leavened. Their portion … … The juxtaposition of the word chelkam (their portion) to the word chametz (leavened) is the reason for the Rabbis’ interpretation that the portion the priests receive from the meal-offering, neither may be baked with leaven. — even the residue [which the priests receive as their share of the meal-offering] may not be baked with leaven. As the sin-offering, and as the guilt-offering — this teaches that just as the sin-offering must come from ordinary money, (further, 16:6), that is, from the money which belongs to him. Sacred money, on the other hand, is not completely his to dispose of as he wishes. and can be offered only at daytime, and the priest performs all its acts with his right arm — so also this meal-offering must come from ordinary money, and be brought at daytime, and its acts must be performed with the priest’s right hand. Every male among the children of Aaron may eat of it — it may be apportioned even amongst those priests who have a bodily blemish [such as are mentioned further in Chapter 21:16-21 as disqualifying them from performing the acts of offering, but they may eat the residue of the meal-offering].
Now with regards to the meal-offering of the priests He added [this command]: And every meal-offering of the priest shall be wholly burnt; it shall not be eaten. On this the Rabbi [Moshe ben Maimon] wrote in the Moreh Nebuchim that the reason [for the meal-offering of the priest being entirely burnt] is because every priest offered up his own meal-offering himself, and if he were to offer it and eat the residue of it himself, it would appear as if he had brought no offering. For nothing was offered of an ordinary individual’s meal-offering (the meal-offering of the individual). except the frankincense and the handful of the flour. If then, in addition to the fact that the whole offering was small, he who offered it were to eat it himself, he would imagine (and he will imagine).” Such is the text in Al Charizi’s translation of the Moreh Nebuchim, which Ramban follows. The intent would seem to be that the priest who is offering his own meal-offering will imagine that he has performed no Divine Service, and therefore he might violate the laws regarding the eating of the residue. Hence the Torah prohibited him from eating it. In Ibn Tibbon’s translation, however, the reading is: “V’lo yeira’eh (and it will not appear),” that is, to others, that a Service has been performed, and therefore they will hold the priest in disregard for eating it. That is why the Torah commanded that it be wholly burnt. that he had brought no offering at all. Therefore [the Torah required] that it be entirely burnt.