Reference for Shabbat 296:1

ניפרוס סודרא אתי לידי סחיטה נכסייה בנכתמא זימנין דמיפסק ואתי למקטריה הלכך לא אפשר

Shall one spread a cloth? then he may come to wring it out. Shall one cover it with a lid? it [the string wherewith it is tied] may break and he will come to knot it.<span class="x" onmousemove="('comment',' With a permanent knot, which is forbidden. ');">¹</span> Therefore it is impossible.

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