The Rebbe's mazkir, Reb Binyomin Klein, related:
Before Sukkos one year, a Crown Heights yungerman entered a small esrog shop and was surprised to see a wealthy acquaintance buying a simple esrog.
The gvir explained that he planned to buy another beautiful esrog, but he bought this one to support the shopkeeper, a chossid who was struggling financially.
On Sukkos morning in 770, however, his friend noticed him using the plain esrog. "I realized," the man explained, "that the most mehudardike esrog is one through which I fulfilled the mitzvah of ahavas Yisroel and helped another Yid.”
The chossid decided to write the entire episode to the Rebbe and gave the note to me.
When I entered the Rebbe's room with this note among other matters, the Rebbe stopped and spent a while reading it. He read the story through, and then read it again and again.
I could see the Rebbe's face light up as he read. The tremendous nachas and satisfaction from the care of chassidim for one another was plainly visible in his face.