Reference for Bekhorot 7:30

כדרבי יהושע בן לוי דאמר ר' יהושע בן לוי

then [the first-born of his asses] should not be released [from redemption]; (for it has been taught: Why is [the word] 'Aaron' dotted in the Book of Numbers?<span class="x" onmousemove="('comment',' Num. III, 39: All that were numbered of the Levies which Moses and Aaron numbered. For all dottings of a word have the purpose of limiting and excluding something.');">²⁰</span>

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