Once Rabbi Levi Yitzchak of Berdichov went traveling to collect money to marry off an orphan girl. He came to an inn where a group of sinners were playing cards. When Rabbi Levi Yitzchak asked them for charity to help the young bride, they began mocking him and asking what they would get in reward for the mitzvah.
“Olam Haba – the World to Come!” he replied.
One man in particular was very derisive and said, “I have no place waiting for me there, anyway!” Then, to add insult to injury, he told Rabbi Levi Yitzchak, “But I will give you all the money you need for her dowry if you sell me your Olam Haba!”
Rabbi Levi Yitzchak immediately jumped at the opportunity and wrote out a contract. The surprised man agreed and signed, giving the rabbi all the money needed to make the wedding.
When the man returned home, he began laughing at what he considered a silly transaction. His wife asked him what had happened, and when he told her, she became livid. “Your Olam Haba?” she screamed. “What little you may have, you sold it?” After a heated argument, she forced her husband, much against his will, to return to Rabbi Levi Yitzchak and ask him to cancel the contract.
Rabbi Levi Yitzchak, of course, refused at first. The man pleaded, but Rabbi Levi Yitzchak kept on refusing. Finally the man begged, “You can keep all the money, but please, please, give me back my portion in the World to Come!” Rabbi Levi Yitzchak then agreed.
With the contract annulled, the man asked Rabbi Levi Yitzchak how much of a portion he, the man, had in the future world. Rabbi Levi Yitzchak replied, “When you first sold me your portion, it truly was not worth very much at all. But now that you’ve donated that sum to marry off an orphan girl, your portion is very, very great indeed!”
From “More Blessed to Give: Rebbe Nachman on Charity”