Reference for Chullin 222:3

אימר דאמור רבנן דיעבד לכתחלה מי אמור

The Rabbis may have permitted it after the act, but did they permit it in the first instance? ' But if a vessel was placed below to collect the drippings, even though the meat was on top of the liver, it is forbidden.<span class="x" onmousemove="('comment',' I.e., the drippings of fat in the vessel are forbidden to be eaten because they are mingled with the blood drippings from the liver.');">¹</span>

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