Reference for Menachot 91:1

שאם הוזקקו זה לזה שמעכבין זה את זה ואיזה הוא זיקה שלהן שחיטה

that if they were attached to each other the [absence of] one invalidates the other.<span class="x" onmousemove="('comment',' I.e., if the two loaves and the two lambs were together in the Sanctuary intended and ready for the Festival-offering, that fact attached them to each other; and therefore if one kind, either the loaves or the lambs, was lost, the remaining kind may not be offered, but must be taken away to be burnt.');">¹</span>

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