Reference for Shabbat 268:18

גופא אמר רב אין מונעין חמין ושמן מעל גבי מכה בשבת ושמואל אמר נותן חוץ למכה ושותת ויורד למכה

Come and hear: One may not pour hot water and oil on a rag which is on a wound on the Sabbath? — There too it is because of wringing out. It was taught in accordance with Samuel: One may not apply hot water and oil to a wound on the Sabbath, but one may put it outside the wound, and it flows down on to the wound.

Jastrow