Shabbos, Perek Kirah, Mishnah 5. This mishnah teaches that although it is forbidden to extinguish a fire on Shabbos, there are certain actions a person may take in order to limit the spread of a blaze.
Spreading a goat hide:
Ben Nanas says that one may spread a goat hide over a "shidah teivah u'migdal" - various types of chests, boxes and cabinets - that have caught fire, and when a person does not want the fire to spread further, he may use these hides to contain it. The reason this is permitted: "mipnei she'ha'esh mecharechet oso" - a hide of this sort does not actually burn but only gets singed, and therefore it can protect the chest, the box and the cabinet from being consumed by the fire.
Making a barrier out of vessels:
One may also make a barrier out of any type of vessel in front of the fire, whether the vessels are empty or full, and even if they are full of water, so that the fire will not spread further. Even though this may cause the vessel to burst and the water to spill out, there is no prohibition involved, since this is 'gerama' - extinguishing indirectly - and that is permitted.
The opinion of Rabbi Yose:
Rabbi Yose disagrees and forbids making a barrier out of new earthenware vessels filled with water, because being new they cannot withstand the fire: they burst and extinguish the fire. His opinion is that 'gerama' is forbidden - extinguishing a fire is prohibited even indirectly, and even in a situation where there will be a financial loss.
In summary: In this mishnah we learned that although extinguishing is forbidden on Shabbos, one may limit the spread of a fire: by spreading a goat hide, which the fire merely singes rather than burns, and by making a barrier out of vessels, whether empty or full. The Tannaim disagree about the law of 'gerama': according to the first opinion it is permitted, while Rabbi Yose forbids extinguishing even indirectly, and even where there is a financial loss.