Reference for Sukkah 49:11

והעוסק במצוה פטור מן המצוה מהכא נפקא מהתם נפקא דתניא (במדבר ט, ו) ויהי אנשים אשר היו טמאים לנפש אדם וגו' אותם אנשים מי היו נושאי ארונו של יוסף היו דברי ר' יוסי הגלילי

And one who is involved in a mitzvah is exempt from a mitzvah comes out from here? It comes from there, as it is taught in a Baraita: (Numbers 9:6) "There were people that were impure by the flesh of man..." Those people, who were they? They were the carriers of Yosef's body, the words of Rabbi Yose HaGlili.

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