Reference for Zevachim 186:20
רבי אלעזר אומר בגד אין לי אלא בגד מנין לרבות שק
AND WHATEVER IS ELIGIBLE TO CONTRACT UNCLEANNESS,<span class="x" onmousemove="('comment',' V. discussion infra.');"><sup>24</sup></span> AND IS FIT FOR WASHING, WHETHER A GARMENT, A SACK, OR A HIDE, MUST BE WASHED. THE WASHING MUST BE IN A HOLY PLACE;<span class="x" onmousemove="('comment',' In the Temple court.');"><sup>25</sup></span> THE BREAKING OF AN EARTHEN VESSEL MUST BE IN A HOLY PLACE; AND THE SCOURING AND RINSING OF A BRAZEN VESSEL MUST BE IN A HOLY PLACE.<span class="x" onmousemove="('comment',' V. Lev. VI, 21: But the earthen vessel wherein it (sc. the flesh of a sin-offering) is sodden shall be broken; and If it be sodden in a brazen vessel, it shall be scoured, and rinsed in water.');"><sup>26</sup></span> IN THIS THE SIN-OFFERING IS MORE STRINGENT THAN [OTHER] SACRIFICES OF HIGHER SANCTITY. <big><b>GEMARA: </b></big>How do we know it? - Because our Rabbis taught: [And when there is sprinkled of the blood thereof upon] a garment:<span class="x" onmousemove="('comment',' Lev. VI, 20.');"><sup>27</sup></span> I know it only of a garment: whence do I know to include the skin, after it is flayed? Because it says, thou shalt wash that whereon it was sprinkled.<span class="x" onmousemove="('comment',' This is a repetition, and intimates extension.');"><sup>28</sup></span> You might think that I include the skin [even] before it was flayed: therefore it states, 'a garment': as a garment is an article eligible to contr uncleanness, so everything that is eligible to contract uncleanness [is included]:<span class="x" onmousemove="('comment',' After a skin is flayed it can be put to use as it is, without further dressing; therefore if its owner expressly intended to use it thus, it is technically a utensil, and subject to defilement. Before it is flayed, however, it cannot be put to use, and cannot become unclean.');"><sup>29</sup></span> these are the words of R'Judah. R'Eleazar said: 'A garment': I know it only of a garment; whence do I know to include a sack