Reference for Chullin 175:22

רבנן סברי

ONE MAY COVER IT UP WITH FINE DUNG, WITH FINE SAND, WITH LIME, WITH A POTSHERD OR A BRICK OR AN EARTHENWARE STOPPER [OF A CASK] THAT HAVE BEEN GROUND INTO POWDER'BUT ONE MAY NOT COVER IT UP WITH COARSE DUNG OR COARSE SAND, NOR WITH A BRICK OR AN EARTHENWARE STOPPER [OF A CASK] THAT HAVE NOT BEEN GROUND INTO POWDER; NOR MAY ONE TURN A VESSEL OVER IT.<span class="x" onmousemove="('comment',' In the Mishnah ed. Lowe there is added here: Nor cover it with stones.');">⁹</span>

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