Reference for Chullin 161:23

וקשיא לן

answered: There is an omission here, and this is how it should read: If both animals were consecrated add [were slaughtered] outside [the Sanctuary]: according to the Rabbis, [he who slaughtered] the first incurs the penalty of Kareth, and the second [animal] is invalid but he [who slaughtered it] is not culpable;<span class="x" onmousemove="('comment',' He has not incurred Kareth since it could not have been offered this day in the Sanctuary.');">⁸</span>

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