This unbelievable story was heard in the name of Rabbi Vishedski A'H.
There was once a chossid of the Alter Rebbe. The man was a peddler of goods and made a living traveling from town to town selling his items. One time, by a yechidus, the Rebbe asked him questions and after hearing the chossid's responses, the Alter Rebbe advised him that he should always carry with him three challahs. The chossid did not understand why the Rebbe would give him such a strange instruction, but the chosid did exactly as the Rebbe instructed, trusting that one day he would understand why he got such advice from the Rebbe.
And so it happened, one day that the chossid was traveling before shabbos and he lost his way. Shabbos was approaching soon so he quickly tried to find a place to stay. He knocked on a house and the owner came out with a friendly smile. They exchanged greetings and the chossid explained to the man that he needed a place to stay the night. The man invited him in and led him to his room. Now, this man was a non Jew, when he opened the door and led the chossid into the room, the chosid realized that there was a friend that was going to be staying with him that night. It was a huge dog the size of the chossid himself! He realized that his host is not as friendly as he first appeared to be and quickly turned around to go back. By this time the door was locked and the non Jew told him that it this room “people go in but they do not come out.”
The chossid became very afraid. He figured being in a room with such a friend he did not have long to live. He started praying to G-d and saying vidui (confession). He noticed that the dog was just sitting in his corner. So the chossid began davening mincha. Still, the dog was quiet. He then davened kabbalas shabbos and marriv. The chossid remembered that he had three challas with him so he found some water in the room, washed and made kiddush on the bread. The dog listening to kiddush, so to speak, and afterwards was very excited. The chossid realized that the dog wanted some challah, so he ate a small piece and gave the dog the rest of the loaf. Needless to say, the rest of the night he did not sleep, with such a friend in the room who would sleep? Morning came and the chossid davened shacharis and the same scene repeated itself with the challah.
After shabbos the owner of the house opened the door to the room carrying a broom and bucket hoping to clean up the bones of the man. Lo and behold he found the chossid sitting in one corner and the dog in the other. So he screamed at the dog, "get that Jew, eat him!” but the dog wouldn't move. The chosid realized that when you feed a dog you become its owner. So he said to the dog “get that man!” and the dog jumped on the non Jew and tore him apart and killed him.
Then the dog took the Jew by his kappota and dragged him to the forest. There he took him to a place where the chosid found a great treasure, a chest filled with gold coins. The non Jew acquired it all by killing and stealing it from his former guests. The dog grabbed the Jew again and took him outside the forest near the village. At that point the dog spread dropped dead. The Jew realized where he was and made his way home. Before going home he stopped by the Alter Rebbe to tell him all that had transpired. The Rebbe took him in and told him the following: the dog was a gilgul (reincarnation) of a Jew who did not properly fulfill the mitzvah of eating after making kiddush. His punishment was to be stuck in the body of this dog. When you made kiddush for him this was its' rectification. The reason he took you to show the gold coins is because he wanted to repay you for helping him accomplish his tikkun so he can go to Gan Eden. The Rebbe told the chosid that he should open a business with the gold coins which the chossid did and became a rich man.
Needless to say, the chossid realized why the Rebbe gave him the seemingly strange instruction to carry the three challahs with him at all times.