Once, during the winter, the Baal Shem Tov was traveling in Russia with one of his great disciples, Rabbi Moshe Shoham, and in Russia during the winter the countryside is usually covered with snow. So they were traveling in a sleigh. One day, they realized that it was the 15th of Shvat, and they had no fruit with which to celebrate the holiday. So the Baal Shem Tov said to drive the sleigh off the main road and into the fields. They went for a short distance and came upon a field that not only was not snow-covered, but had in it an orchard of oranges; moreover, it not only was not cold there, the climate was tropical! They immediately went over, picked some of the oranges, and joyfully made the blessings, including shehechayanu, to celebrate the holiday.
Rabbi Moshe Shoham also took a few oranges back to the sleigh, to have for later. All this time, he did not even wonder where does an orange orchard, with a tropical climate, appear suddenly in the Russian countryside in the middle of winter! Oranges do not grow in Russia! Being often around the Baal Shem Tov he was so used to miracles that such events did not even cause him to marvel!
As they started back to continue their journey, Rabbi Moshe regretted that he had not taken even more oranges. When they got back to the main road, for one reason or another, the Baal Shem Tov decided to rest briefly, and Rabbi Moshe took the opportunity to return to the orchard. He followed the path of the sleigh tracks to that field, but when he reached it, there was no orchard!
When he returned to the sleigh, the few oranges he had picked and had put in the sleigh had also disappeared. When he asked the Baal Shem Tov about this, the Besht told him, "When I felt unhappy about having no fruit and not being able to celebrate Tu BeShvat, I brought-- by mystical means-- an orchard from the Land of Israel here. But since the whole point was to perform a mitzvah, not for personal benefit, the orchard and the few fruit you had taken disappeared afterward."