Pesachim 78A

אלא, לא קשיא: כאן ⁠— ביחיד, כאן ⁠— בציבור.

Rather, it is not difficult: There, where R' Yehoshua said that it is invalid ab initio, he was referring to the offering of an individual. Here, in the Mishnah, which states that it may be sacrificed even ab initio, it is referring to an offering involving the public.

נימא מתניתין דלא כרבי יוסי. דתניא, רבי אליעזר אומר: הציץ מרצה על אכילות. רבי יוסי אומר: אין הציץ מרצה על אכילות.

The Talmud asks: should we say that the Mishnah is not in accordance with the opinion of R' Yosei? As it was taught in a baraita: R' Eliezer says that the frontplate appeases God for the impurity of portions of offerings that are supposed to be eaten. R' Yosei says that the frontplate does not appease God for the impurity of portions of offerings that are supposed to be eaten; it appeases God only for the impurity of the parts of offerings that are burned on the altar.

קא סלקא דעתך מדקאמר רבי יוסי: אין הציץ מרצה על אכילות ⁠— כרבי יהושע סבירא ליה, דאמר בעינן תרתי. נימא השתא מתניתין דלא כרבי יוסי?

The Talmud explains the question: It could enter your mind to say: From the fact that R' Yosei said that the frontplate does not appease God for the impurity of portions of offerings that are supposed to be eaten, it can be inferred that he holds in accordance with the opinion of R' Yehoshua, who said that we require the two parts of the offering, the blood and the meat, to be valid. If this were not the case, it would be sufficient for the frontplate to appease God for the impurity of the blood, and it would not be necessary for the frontplate to appease God for the impurity of the portions of offerings that are supposed to be eaten. Let us now say that the Mishnah is not in accordance with the opinion of R' Yosei.