Mishnayos Shekalim Perek 8 Mishnah 3

שוחט בה מיד – for certainly, its owner immersed it [in a ritual bath] from yesterday in order that it would have a sunset (required after purification, to be deemed entirely clean) and that it would be appropriate to slaughter with it on the day of the Eve of Passover.

בשלשה עשר שונה ומטביל – meaning to say, even though it is possible to state that its owner already immersed it [in a ritual bath], the person who finds it must immerse it a second time for perhaps, its owner had not immersed it and they had a while to wait until it was close to darkness, and even though they did not decree on doubtful utensils in Jerusalem because the stringency of holy objects required immersion for it. But Maimonides explained [the word] "שונה" /”a second time,” to mean to sprinkle upon it for it had become ritually impure through contact with the dead, and he sprinkled [from the ashes of the red heifer] on the third day (see Numbers 19:12), and now sprinkles once again upon it and afterwards immerses it.

בזה ובזה – whether on the thirteenth or the fourteenth [of Nisan].

שונה ומטביל – he immerses it again for the hatchet/curved cutting tool is not appropriate other than for the Hagigah/the Festival Offering for the breaking of a bone is permitted on it, and in the Gemara of Pesahim (Tractate Pesahim 70b) establishes that at the time when the Nasi/head of the Sanhedrin is on his deathbed on the thirteenth [of Nisan], for if he would die, the entire community will be ritually impure and will sacrifice the Passover offering in defilement, but they would not to ritually purify the utensils; therefore, the knife that one needs for the slaughtering of the Passover offering – this is one doubt, for perhaps the Nasi won’t died and they will make the Passover offering in ritual purity, they immerse it and there is a presumption that they purified it on the thirteenth day in order to slaughter the Passover offering on the fourteenth. Bu the hatchet/curved cutting tool, there are two doubts: a) perhaps the Nasi will die and they will make the Passover offering in a state of ritual defilement and they don’t bring the Hagigah/Festival offering, and there is no need for the hatchet/curved cutting tool, and even if he doesn’t die, perhaps the Passover offerings are many and they don’t do the Hagigah/Festival Offering on the fourteenth; therefore, they don’t immerse it and b) it has the presumption that it they did not purify it.

חל י"ד להיות בשבת שוחט בה מיד – but we don’t say that since it is Shabbat, we will not slaughter it out of a doubt that perhaps it was ritually impure and it is found that the Passover offering was ritually impure, and we desecrate the Sabbath not at the place of a commandment. But my teachers explained that we slaughter it immediately with a hatchet/curved cutting tool stating that even though there is no Festival offering/Hagigah on the Sabbath, nevertheless, there is a presumption that he immersed it from the Eve of the Sabbath (i.e., Friday) for the need of the Festival offering/Hagigah on the fifteenth [of Nisan].

בחמשה עשר שוחט בה מיד – because the entire people knows that sprinkling and immersion are prohibited on the Jewish festival/Yom Tov, and we immerse everything from before the Jewish festival.

נמצאת – the hatchet/curved cutting tool

קשורה לסכין – is tied to the knife. We stated that it was definitely immersed with the knife, but Maimonides explained that it is found that an undefined knife is tied with another known knife, it is like the known knife; if it (i.e., the known knife) is ritual impure, it (i.e., the other knife) is ritually impure; if it (i.e., the known knife) is ritually pure, it (i.e., the other knife) is ritually pure.