Reference for Chullin 257:13

הרי מטמא טומאה חמורה אגב אביו

The uncleanness thereof [I say] is not decreed by the law of the Torah; for should you say it is so by the law of the Torah then we should have a case of foodstuffs being able to convey the graver uncleanness [later on]!<span class="x" onmousemove="('comment',' Which would conflict with the principle laid down supra 121a, quoted supra p. 725, n. 5.');">⁹</span>

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