Reference for Pesachim 91:13

<big><strong>מתני׳</strong></big> כיצד מפרישין חלה בטומאה ביו"ט

and one of them is tanning. For we learned: And all these, if he tanned them or trod on them to the extent of tanning,<span class="x" onmousemove="('comment',' Hides were spread out to be trodden on, and this was part of the tanning process.');">¹⁶</span>

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