Menachos, chapter nine, mishnah 6. This mishnah addresses the question of which offerings require nesachim (wine libations).
The text of the mishnah:
"Kol korbenos hatzibbur v'hayachid te'unin nesachim, chutz min habechor v'hama'aser v'hapesach v'hachatas v'ha'asham, ela shechataso shel metzora v'ashamo te'unin nesachim" - all communal and individual offerings require libations, except for the firstborn, the tithe, the Pesach offering, the sin offering and the guilt offering; however, the sin offering and guilt offering of a metzora do require libations.
The mishnah opens with a broad rule: all offerings require libations, whether they are communal offerings or individual offerings. It then lists the exceptions, and the list is somewhat surprising, since in fact it includes most categories of offerings:
Habechor - the firstborn male animal.
Hama'aser - the tenth animal set aside from the flock each year.
Hapesach - the Pesach offering.
Hachatas - the sin offering.
Ha'asham - the guilt offering.
To this list the mishnah adds one exception: there is one sin offering and one guilt offering that do require libations - those brought by the metzora.
The reason for the metzora's exception:
The Rambam offers a reason: the sin offering and guilt offering of the metzora do not come to atone, as ordinary sin offerings and guilt offerings do; they are only part of the purification process. Others base the ruling on a decree of Scripture, derived from verses.
What emerges is a simple rule: the olah and the shelamim - and the todah, which is a subcategory of shelamim - require libations; the remaining offerings do not require libations, except for the guilt offering and sin offering of the metzora.
A question on the wording of the mishnah:
Why does the mishnah use the language of "all offerings" requiring libations, when in fact there are many categories of offerings that do not require them? After all, five of the eight categories of animal offerings do not require libations, and only three of them do. If so, it is puzzling that the mishnah states that all of them require libations.
The answer to this question is not clear. What follows is only a personal theory, one that is not received from any other source but is offered here as a suggestion.
The theory is this: in terms of the actual number of animals that pass through the gates of the Beis HaMikdash, the overwhelming majority are brought as olos and shelamim. These are by far the most common offerings, and they are in fact the only voluntary ones, since everyone who comes up to the Beis HaMikdash brings olos re'iyah and shalmei chagigah and the like. It turns out that the volume of offerings tilts heavily toward the types that require nesachim, while the remaining offerings are, as it were, more exceptional cases. Therefore, even though the number of categories of offerings that do not require nesachim is greater, most of the animals that enter the Beis HaMikdash do in fact receive nesachim.
In summary: In this Mishnah we learned the rule that all communal and individual offerings require nesachim, and the exceptions that do not - the bechor, the ma'aser, the pesach, the chatas and the asham - except for the chatas and asham of a metzora, which according to the Rambam do not come to atone but rather as part of the purification process. We considered the question of why the Mishnah used such sweeping language, and offered an explanation based on the actual volume of offerings - but the door remains open for a better one.