Reference for Chullin 58:25

ואי אמרת ישנה לשחיטה מתחלה ועד סוף לפלוג נמי בשחיטתה

If any invalidating defect befell it during the slaughtering it does not render unclean the garments worn by those who, either before or after the [occurrence of] the defect, took part in any service in connection with it.<span class="x" onmousemove="('comment',' The reason being that so long as it has not been validly slaughtered it can in no wise be regarded as the Red Cow, and therefore all the rules of uncleanness stated in connection with it do not apply.');">¹²</span>

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