Reference for Shabbat 268:14

אמר להו ההוא מרבנן ורבי יעקב שמיה מסתברא הרחצת כל גופו דאי ס"ד הרחצת מילה מי גרע מחמין על גבי מכה דאמר רב אין מונעין חמין ושמן מעל גבי מכה בשבת

To this R. Dimi demurred: And whence [does it follow] that they differ here in respect of hot water heated on the Sabbath? Perhaps they differ in respect of hot water heated on the eve of the Sabbath? — Said Abaye, I wanted to answer him, but R. Joseph anticipated [me] and answered him: Because it is a danger for him.<span class="x" onmousemove="('comment',' Hence the Mishnah must certainly refer to water heated on the Sabbath. ');">¹²</span>

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