Makkos, Chapter 3, Mishnah 9. The previous Mishnah dealt with receiving multiple sets of lashes for a single prohibition, and our Mishnah deals with the other side of the coin: a single act in the course of which a person violates several different prohibitions, and is liable to several sets of lashes for them.
"Yesh choresh telem echad v'chayav alav mishum shemonah lavin":
There can be a case in which a person plows a single furrow in a field, and through that very act he violates eight Torah prohibitions. And these are they:
"Hachoresh b'shor u'chamor" - the plow is drawn by an ox and a donkey together, and immediately there is a violation of the prohibition of kilayim of animals - performing labor with two different species simultaneously, as it says: "You shall not plow with an ox and a donkey together."
"V'hein mukdashin" - the ox was consecrated as an offering, and the prohibition in this is "You shall not work with the firstborn of your ox" - it is forbidden to work with a firstborn ox, and from here we learn regarding the other offerings as well, that one may not work with an animal that was consecrated as an offering.
The donkey, which is not a kosher animal and cannot be brought as an offering, is a case where it was consecrated for the upkeep of the Temple - it belongs to the Beis HaMikdash for its needs and its funds, and there is a prohibition of me'ilah with it, not to derive benefit from it. This prohibition is derived from the verse in Devarim, "You shall not work with your ox," that one may not derive benefit from it.
Kilayim in a vineyard - the plowing covers over a seed of wheat, a seed of barley and a grape pit, and joins them together, and this is kilayim of the vineyard.
Shevi'is - the plowing is done in the Shemittah year, which is forbidden by Torah law.
Yom Tov - the day on which he plows is Yom Tov. The Mishnah says Yom Tov and not Shabbos, because on Shabbos a person does not receive lashes: one who acts intentionally is liable to the death penalty, whereas for Yom Tov he receives lashes.
A kohen in a beis haperas - the field is a beis haperas, which has the status of a cemetery, and the one plowing is a kohen, who is forbidden to enter a cemetery.
A nazir in a beis haperas - that same person is also a nazir, who is forbidden to become tamei.
In all, eight prohibitions in a single act.
The dispute between Chananyah ben Chachinai and the Sages:
Chananyah ben Chachinai says: "Af halovesh kilayim" - if at that moment the one plowing is wearing a garment of shaatnez, this is a ninth prohibition.
The Sages said to him: "Eino hasheim" - this is not part of the same matter, but rather an entirely separate prohibition. Wearing kilayim is a different prohibited act that has no connection whatsoever to the act of plowing.
Chananyah ben Chachinai answered them: the fact that the person is a nazir is likewise not relevant to the act of plowing itself, so why is it counted?
Rather, the view of the Sages is that when the person is a kohen or a nazir, he cannot reach the act of plowing at all without entering the beis haperas and becoming tamei, and therefore by its very definition the act of plowing includes the prohibition of becoming tamei. Not so with wearing kilayim, upon which the plowing is not dependent.
In summary: in this Mishnah we learned that a single act of plowing one furrow can include eight prohibitions: kilayim of animals, working with consecrated animals and me'ilah with animals consecrated for the upkeep of the Temple, kilayim of the vineyard, Shevi'is, Yom Tov, and the tumah of a kohen and of a nazir in a beis haperas. We also learned the dispute between Chananyah ben Chachinai and the Sages regarding wearing kilayim, and the distinction between a prohibition bound up with the very act of plowing and one that is separate from it.