Reference for Bekhorot 50:21

נשחטו אסרי רבנן

R'Shesheth raised an objection: Blemished sacrifices [which became mixed up] with other sacrifices are forbidden whatever they may be;<span class="x" onmousemove="('comment',' No matter how few in number, so that even if one blemished animal became mixed up with a thousand. all are rendered unfit for sacrificial purposes.');">¹³</span>

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