If one separated an animal to be used as a purification offering, but then lost it, and he brought another animal in its place, and then found the first one, it should die. If one separates coins to be used [to purchase] a purification offering, then lost them, and bought an offering with [other coins], and then found the [original] coins, they should be brought [i.e., thrown into] the Salt Sea.
Tractate Temurah deals with substitutions—what happens when one animal is brought to the Temple in place of another as a sacrifice? The first animal has already been designated for sacred service, and cannot simply be used for normal needs. Yet if the sacrifice was a chatat (purification offering), and the owner has already been purified, what should be done with the first animal? This mishnah says that no benefit can come from an animal or coins once they are designated for God. According to the Talmud (Kiddushin 55b), the former animal was left to die in a barn without food.