Reference for Bekhorot 113:14

ר' יהושע אומר

An objection was raised: And likewise if partners divided [an estate] and one took ten lambs and the other took nine with a dog, [the lambs] taken against the dog are forbidden [for the altar]<span class="x" onmousemove="('comment',' Because one of them is the exchange for the dog, and as we do not know which, therefore all are prohibited for the altar.');">¹⁰</span>

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