Reference for Chullin 200:29

על כזית מן המת מגלח על המת כולו לא כ"ש

And this is precisely implied [in the teaching of the Mishnah]: R'JUDAH ARGUED, WAS NOT THE SCIATIC NERVE PROHIBITED FROM THE TIME OF THE SONS OF JACOB, AND AT THAT TIME UNCLEAN ANIMALS WERE STILL PERMITTED TO THEM?

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