One year, there was a severe shortage of beautiful Esrogim, and none of the specimens brought to the Holy Divrei Chaim of Sanz ztza"l met his approval. His devoted gabbaim selected two distinguished emissaries, gave them a large sum of money, and sent them to major cities to find an exceptionally fine Esrog for the Rebbe. With Hashem's help, they located a breathtaking Esrog. Though the seller demanded a fortune, they paid without negotiating, overjoyed to have secured such a specimen for the Sanzer Rebbe.
On their journey back, they stopped at the home of a wealthy rural Jewish merchant who traded in live fish. They showed him the magnificent Esrog they had bought. Looking at his fish tanks, the emissaries recalled that there were currently no fresh fish available in Sanz, meaning the Chassidim would have to serve salted herring for the holiday meals. They asked to purchase several live fish to honor the Rebbe's festival table, but the man replied that his supply was low and he could not sell them any.
The emissaries pleaded and offered a large sum of money, but the merchant replied that he did not need money. However, he made an offer: he possessed one extraordinarily large live fish-enough to feed the entire court for the holiday-and he would trade it to them in exchange for the Esrog.
The emissaries calculated that since the first day of Succos coincided with Shabbos that year, fresh fish held immense spiritual importance for Oneg Shabbos. Furthermore, the biblical requirement for an Esrog on the Shabbos is deferred to the second day in post-Temple times. They agreed to the deal, loaded the giant fish into a large barrel of water on their wagon, and set off.
When they arrived in Sanz, the gabbaim and Hasidim rushed out to see the Rebbe's Esrog. When the emissaries announced they had traded the Esrog for a massive fish, the gabbaim were furious at what they considered immense foolishness. Humiliated, the emissaries fled to a nearby village to spend the holiday, leaving the fish behind in Sanz.
The large fish was prepared for the festival meals, while the attendants decided not to inform the Rebbe of what had transpired. However, nothing was hidden from the holy tzaddik. To the astonishment of the gabbaim, when the fish was served at the Friday night meal, the Sanzer Rebbe remarked:
"My heartfelt thanks to the devoted emissaries who had the wisdom to realize that since the first day of the festival falls on the Shabbos, having fresh fish for the holiday meal is of paramount importance. This year, the Esrog requirement is Rabbinic, whereas serving fish fulfills two distinct commandments: 'And you shall rejoice in your festival' and 'And you shall call the Shabbos a delight.' "
The Rebbe took a large portion of fish, instructed the gabbaim to set it aside, and ordered them to locate the two emissaries after the Shabbos to deliver the portion and request their forgiveness. On Saturday night, the gabbaim traveled to the village, presented the Rebbe's shirayim to the emissaries, and apologized. The emissaries returned to Sanz with great joy.
The joy was compounded later that night when the fish merchant himself arrived in Sanz, carrying the Esrog. He placed it directly into the holy tzaddik's hands, explaining that his true intention had been to honor the tzaddik with both the fish and the fine Esrog!