The following story is an example of mesirus nefesh for the mitzvah of ahavas Yisrael and the benefits that can be earned from it. I heard the story from the baal hamaasah, a respected rav in America who is involved in kiruv rechokim.
One day, his wife told him that she wanted to donate a kidney to help someone on dialysis. Her husband tried discouraging her, but she insisted she wanted this zechus.
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.
The husband asked the Rebbe, "The sick patient needs the kidney as quickly as possible, but our child's chasunah is coming up soon. Should we do the surgery now or wait until after the chasunah?"
The Rebbe told them that if the doctor says she will recover in time for the chasunah, she should proceed with the surgery now.
They 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 would be back on her feet in time for her child's chasunah.
The doctors began with the standard battery of tests to confirm that she was a healthy donor candidate. During one of the tests, they discovered that she had a tumor right beneath one of her kidneys, pressing on a primary artery that sends blood to the heart. Had the tumor gone undetected, it could have blocked the blood circulation. She thought she was saving another person's life, but she saved her own. Because of her ahavas Yisrael, her life was saved.
