Kiddushin 54a, Tosafot "Mo'alin"
New Sheqalim can be misused, Old Sheqalim cannot etc. This is the way the sheqalim were brought on the first of Adar the call was sounded to bring sheqalim, and all through that month they used to bring their sheqalim to the lishka until the "approach" to the Holiday of Pesah, i.e., the first of Nisan, and they would make of them a first contribution, for there were three times during a year when they would contribute on the "approach" to Pesah, on the "approach" to Shavu'ot and on the "approach" to Sukkot. In other words, all the sheqalim brought from the first of Adar to the first of Nisan are given in the lishka, and a first contribution is made from them in three containers of 3 se'ah, from which all public sacrifices were paid for until the "approach" to Shavu'ot, as needed. There is a disagreement [amongst tanna'im] concerning the sheqalim left over from the three containers there (in Sheqalim, ch. 4, mishna 4) one says that they are used to make the metal plate coating the altar, while another says they are used to pay for the extra sacrifices on the altar, and whatever is left over from the lishka after the filling of the containers were used for the city wall and towers.
From Nisan on, anyone bringing his sheqel puts it in "Tiqlin Hadtin", i.e., in special containers by that name, broad at the bottom and narrow at the top; they were called "Tiqlin Hadtin" because the sheqalim put in them were new sheqalim of the current year. And when the first of Sivan rolls by, i.e., the "approach" to Shavu'ot, a second contribution is made, in which sheqalim which had been brought in "Tiqlin Hadtin" are put into the same three containers for the offering up of public sacrifices until the approach to Sukkot, at which time a third contribution is made for the offering up of public sacrifices until the first of Nisan, and if the third contribution is not enough [to last] until Nisan, this is the subject of the disagreement there (ibid., 6a) one tanna thinks "he must contribute again", i.e., from the "Hadtin" which were given between Sukkot and Pesah, while from the sheqalim left over after the containers were filled up no contribution is ever made; but R. Meir thinks that "he takes from those left over and from those which were given after the three periods of contribution, i.e., between Sukkot and Nisan.
It is not clear from Rashi's commentary whether they can be misused or not. It is true that R. Yitzhaq ben Avraham explained that new sheqalim can be misused according to R. Yehuda even after the entire contribution, in case they need them finally for the offering up of the sacrifices. This was also declared in Tractate Sheqalim (ibid.) regarding the containers, as it says there When the third is finished, i.e., when the third is emptied, he goes back to the second; when the second is finished, he goes back to the first; when all three are finished, he makes a new contribution, i.e., from "Tiqlin Hadtin" which were brought after Sukkot, and should not do so from those left over from the lishka. R. Meir says he should go back to the leftovers, for R. Meir used to say Those left over can be misused, as they may be needed in the end. And now he thinks like the tanna who says he must go back and make another contribution, and so new sheqalim, i.e., Hadtin, can be misused, for they may be needed, but this is not so for old sheqalim, i.e., other containers upon which is written "Tiqlin 'Atiqin", for a person who did not bring his sheqalim last year brings them next year and puts them in this container, and they cannot be misused for they are considered the leftovers of the lishka, and they are used to repair the city walls and their towers. R. Meir says Old sheqalim, too, can be misused, for R. Meir used to say The leftovers of the lishka can be misused, and he reasoned there as follows If they (the containers) were all finished, he would go back to the shirayim, the remaining sheqalim of the lishka, and they resemble each other for just as he goes back to the shirayim, so they go back to old sheqalim if they are needed.
Now if one asks, how can old sheqalim be used for public sacrifices, as a new contribution is required (as we learn in Rosh Ha-Shana 7a the money for the monthly New Moon sacrifice is taken from a new contribution), the answer is that this refers to the mitzva (i.e., a priori), but we are considering a case where it is impossible. Furthermore, as long as the sheqalim were brought this year, i.e., less than a year has transpired since they were brought, we can certainly call it "a new contribution", and this way everything works out well.
Another problem everyone raises is that in Tractate Sheqalim (7a) it says The stones of the altar and the courts and the inner Temple can all be misused, and this is dealt with there as follows Since when can shirayim be misused? For these are all made from shirayim! If you then say that this is according to R. Meir, for he said that shirayim can be misused, the problem is that R. Meir was referring to shirayim less than a year since they were brought, whereas here we're dealing with a time-span of over a year, since the altar and Temple were repaired for a number of years this is the problem, for if R. Meir said there that old sheqalim can be misused, even if over a year has passed since they were brought, we can now establish what was learned in Tractate Sheqalim according to his reasoning, but what do we do there with R. Meir according to what we have explained here, that they are called "a new contribution" because they were brought within the past year, which is fine, but then we are unable to explain the case there according to R. Meir.