Here is the much loved story about Guru Nanak and Sacha Sauda, or "True Bargain." I have taken it from http://www.panthic.org/articles/3309
Sacha Sauda or True Bargain - A Story of Guru Nanak
At the age of eighteen, Guru Nanak Sahib Ji, was sent by his father Bhai Mehta Kalu Ji to the city to do business. His father was disappointed that Guru Sahib's mind was not into farming and other worldly work, therefore, he thought perhaps engaging him in trade would firstly, be a good profitable profession, and secondly his son would be happy all day talking to his clients about his business.
Thinking this way and choosing an auspicious day, he called Bhai Mardana Ji to accompany Guru Sahib. "What about Bhai Bala Ji? I heard from our Gurdwara Giani Ji that Bhai Bala Ji accompanied Guru Nanak Ji." Historically there is no such character called "Bhai Bala Ji" who was the companion of Guru Nanak Sahib. Yes, I am sure there were many Bhai Balas. But there was no Bhai Bala Ji as described by "Sants," "Babé," or misguided parchaariks (preachers). There are historical sources from the times of Guru Nanak Ji, such as land records and local government writings, which includes the name of Guru Nanak Sahib Ji, Bhai Mardana etc, however no Bhai Bala Ji. This article is not intended to be on the issue of Bhai Bala Ji, therefore I will not go deeper into the discussion.
Pita Kalu Ji gave twenty rupees to Bhai Mardana Ji and said, "Go with Nanak. Buy and bring some genuine goods by selling of which we may make profit. In this way if you make a profitable transaction, next time I will send you with more money to buy goods."
Guru Nanak and Bhai Mardana Ji started from Talwandi towards Choohar-khaana to purchase some merchandise. They had hardly gone ten or twelve miles from the village when they came across a village affected by disease, where the people were thirsty, hungry and sick due to lack of water and an outbreak of disease. Guru Nanak Sahib Ji said to Bhai Mardana Ji, "Father has asked us to carry out some profitable transaction. No bargain can be more truly profitable than to feed and clothe these naked and hungry children and adults. I cannot leave this true bargain. It is seldom that we get an opportunity to carry out some profitable transaction like this." Guru Nanak took all the money from Bhai Mardana Ji and took it to the next nearest village dwelling, where he bought plentiful supply of food and brought water for the disease-ridden village. Guru Sahib invested the twenty rupees into what we today call "Langar."
Someone reading this may be confused and thinking, "I was told by Giani Ji at the Gurdwara that Guru Nanak Sahib Ji fed hungry Sadhus (group of hermits) sitting in the jungle." Why are we confused? If we read Gurbani, contemplate Gurbani, and understand our Guru, then how can we be possibly confused? The sad thing is that we have for too long relied on "Saadhs," "Sants," "Babé," and ignorant parchaariks to tell us what Guru Ji says, what Guru Jis teaches, and how Guru Ji lived his life. We use little or no rationality or logic to verify whether what we are being told actually collates with the rest of history, with Gurbani or with facts! Yes, this is why we are confused.