Reference for Bekhorot 97:21

אמר רב אשי

and did not leave us to infer this [from the expression 'and upward'] in the Book of Numbers, we have therefore two verses<span class="x" onmousemove="('comment',' That in the Book of Numbers in connection with the census of the first-born of Israel and that in connection with the law of valuation.');">¹⁹</span>

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