From: Rabbi Moshe Sofer
To: Rabbi Yisrael
The Chasam Sofer corrects his student on the prohibition against offering a kosher animal that nursed from a treifah, establishing that the prohibition stems from sevara (disgrace) rather than a biblical verse. He further resolves the Shaar HaMelech's difficulty with the Rambam by proposing that 'min habakar' is a genuine biblical derivation only for derusah — the one treifah explicitly stated in the Torah — while all other treifos known through halacha leMoshe miSinai are excluded via 'hakriveihu na lefachasecha'.
Source: Shu"t Chasam Sofer YD §72