The following story is an example of mesirus nefesh for the mitzvah of ahavas Yisrael and the benefits that were earned from it. I heard the story directly from the baal hama'asah, a respected rav in America who is also involved in kiruv rechokim.
One day, the rav’s wife told him that she wanted to donate a kidney to someone suffering from kidney disease and was undergoing dialysis. Her husband was against the idea, but she insisted that she wanted this zechus. So, they went to the Skverer Rebbe shlita and sought his counsel.
The Rebbe told the husband to respect his wife's wishes because it is a great mitzvah to save a life. The husband asked, "When should she have the operation? I know the ill patient needs the kidney as soon as possible, but our child's chasunah is coming up..."
The husband wanted to push off the procedure until after the chasunah. His wife, however, had rachmanus on the suffering person and wanted to have it done before the chasunah.
The Rebbe told them to discuss it with the doctor. If he said she would be better in time for the chasunah, she could go ahead with the procedure.
The couple consulted with the doctor, and he agreed to speed up the prep stages and do the transplant as quickly as possible, so that the mother could recuperate in time for her child's chasunah.
Kidney donors undergo a series of tests to verify that they are healthy candidates and that their organs are suitable for transplanting. The doctors began performing the standard battery of tests and discovered that the rav’s wife had a growth right beneath one of her kidneys.
The growth was pressing on a primary artery that sends blood to the heart. If the doctors hadn’t done those tests, it is likely the growth would eventually have blocked the blood flow to her heart, and her life would have been in danger. It is doubtful she would have lived to see her child's wedding. Because of her ahavas Yisrael, her life was saved. (She was disqualified as a donor, but another compatible donor was found, so the patient had the transplant performed.)
