Reference for Chullin 70:1

שמא תשב עליהן אשתו נדה אבל בפירי לא אמרינן

for it is feared that his wife when in a menstruous condition sat upon these clothes;<span class="x" onmousemove="('comment',' This being a frequent and common source of uncleanness, greater precaution is therefore necessary with regard to consecrated things, so that clothes which are deemed clean for terumah may yet be deemed unclean for consecrated purposes.');">¹</span>

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