Once upon a time Guru Nanak Dev Ji happened upon Saidpur, the village of Malik ('master') Bhago and Bhai ('brother') Lalo.
Bhago was a rich man. Lalo, a simple carpenter.
Guru Nanak Dev Ji was asked by both to have a meal at their homes. Guruji declined Bhago's feast to dine at Lalo's humble abode.
The rebuffed Bhago asked Guruji, "Why have you refused my offer? I am rich and Lalo is but a poor man."
Guruji answered by taking the roti from Bhago's house in one hand and the roti from Lalo's house in another. He closed his fists. From one hand spurted blood and the the other milk.
Guruji showed Bhago that the riches he coveted were obtained by bullying and stealing from other people, hence his roti was tainted with blood. While Lalo, although poor, was an honest and hard-working man and the fruits of his labor were life-sustaining and sweet, like the milk.
The morals of the story are:
1) the ends don't justify the means.
2) God is omniscient.
3) If you're full of shit, eventually someone's going to call you on it.
Here are some references:
4) My nani <3