Reference for Pesachim 33:12
גופא רב תני משקי בית מטבחיא ולוי תנא משקי בי מדבחיא
Now according to Levi, it is well if he holds as Samuel, who said, They are clean [only] in so far that they cannot defile other [objects]. but nevertheless they are unclean in themselves: then it is possible where they all touched the first.<span class="x" onmousemove="('comment',' Thus: in the first question Haggai asked about successive stages of defilement, and they answered that the oil is clean, since it touched the wine, which as a liquid of the altar can be defiled (i.e.. made unfit) but cannot contaminate. But in the second question each touched the first mentioned, viz., 'one that is unclean by a dead body', and they rightly answered that they are unclean.');"><sup>15</sup></span>