Reference for Chullin 279:40

אי לשילוח בעי לאתויי לבי דינא וקיומי (דברים יג, ו) ובערת הרע מקרבך

If for the one that must be set free, but surely the Torah would not enjoin to set it free if it would thereby lead to transgression! Rather it could serve for the one tha must be slaughtered,<span class="x" onmousemove="('comment',' The term 'clean' is therefore necessary to exclude such a bird from use in the purification rites of the leper.');">²⁹</span>

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