Yadayim, Chapter 4, Mishnah 2. By this point Maseches Yadayim has moved on from the tumah of hands altogether, and the fourth chapter serves as a collection of halachos that were declared "bo bayom," on that day. The day referred to is the famous one on which the sages placed Rabbi Elazar ben Azaryah at the head of the academy, a day on which every halachic question that had been left hanging was brought to a decision. Our mishnah preserves one of the rulings of that day, and its subject carries us far from hands and their washing into a wholly different field of Torah, the laws of the korbanos.
The mishnah begins by reporting the ruling of that day: "Bo bayom amru, kol hazvachim shenizbechu shelo lishmon, kesheirim." Every sacrifice slaughtered "shelo lishmon," not for its own name, meaning that the animal had been consecrated as one category of korban but the shechitah was carried out with a different category in mind, retains its status as a valid offering. It is not rendered pasul; the blood is presented and the designated portions are burned exactly as the halachah requires for that korban. What is lost is something else, as the mishnah continues: "ela shelo alu labe'alim", it does not count for the owner, "lesheim chovah," toward the obligation he had. In other words, the animal itself is fine, yet the man who brought it still stands where he stood before, and he will have to bring a second korban to discharge his duty.
To this general rule the mishnah records two exceptions: "chutz min haPesach umin hachatas." The Pesach offering and the chatas, the sin offering, are not merely ineffective when slaughtered under the wrong name, they are outright invalid.
The mishnah now sharpens the two exceptions: "HaPesach bizmano, vehachatas bechol zman." A Pesach becomes pasul through the wrong designation only when it is offered during its own appointed season, while a chatas is ruined by a wrong designation no matter when it is brought.
"Rabbi Eliezer omer, af ha'asham." Rabbi Eliezer wishes to place a third korban alongside those two, the asham, the guilt offering. On his view the formula would run: "haPesach bizmano," the Pesach when offered in its season, "vehachatas veha'asham bechol zman," while both the chatas and the asham are disqualified by a wrong designation at any point in the year.
Now the mishnah presents a testimony from Rabbi Shimon ben Azzai, whose received tradition also closed the third chapter of this maseches. He introduces it with the words "mekubal ani," I hold it as a tradition, "mipi shivim ushnayim zakein," from the mouths of the seventy two elders, and he fixes the date: it was heard on the very day when the assembly installed Rabbi Elazar ben Azaryah in the seat of the academy. What ben Azzai transmits is this: "shekol hazvachim hane'echalim," that all sacrifices whose meat is eaten, "shenizbechu shelo lishmon," if slaughtered under a designation other than their own, "kesheirim," remain valid, "ela shelo alu labe'alim", without counting for the owner, "lesheim chovah," as the fulfillment of his obligation, "chutz min haPesach umin hachatas," the Pesach and the chatas alone excluded from the leniency.
Finally the mishnah weighs how faithful ben Azzai's report was to what he had received: "Lo hosif ben Azzai", the only thing ben Azzai supplied beyond the tradition itself, "ela ha'olah," was the olah, the burnt offering, and on that single addition, which came from his own reasoning rather than from the elders, the chachamim refused to agree with him.
The Bartenura's comment here is remarkably short and strictly practical. He writes: "Mishnah zo," this mishnah, "bischilas maseches Zevachim," at the very opening of Maseches Zevachim, "hi shenuyah, vesham peirishnuha", it appears there word for word, and he supplied his explanation of it in that location. His point is simply that this mishnah calls for no fresh commentary here.