Mishnah Berura, volume Orech Chaim, section 297, subsection 4
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משנה ברורה סימן רצז ס"ק ח
על ההדס - פי' דשל לולב כיון דאיתעביד ביה חדא מצוה ליעביד ביה מצוה אחריתא... ומש"כ כל היכא דאפשר היינו כל היכא [יא] שיש בו עוד ריח קצת מצוה לכתחלה להדר אחריו וכ"כ בזוהר
[One should say the blessing over spices in Havdallah] over a myrtle branch. i.e., one that was taken together with a lulav on Sukkot. For since one mitzvah was already done with the myrtle-branch, one should use it for another mitzvah...The phrase in the Shulchan Aruch, 'wherever this is possible,' means that as long as it has somewhat of an odor it is a mitzvah, initially, to search after and use it. So too, writes the Zohar. [Translated by Rabbi Aviel Orenstein]
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Suggested Discussion Questions:

What can this source teach us about sustainable resource use?

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Time Period: Modern (Spinoza through post-WWII)