Laxmi and Daridra were sisters. While Laxmi virtues, Krishna married Laxmi, Laxmi asked Krishna to find a suitable husband for Daridra. Krishna said, "No body would like to marry her because of her laziness." Laxmi said a sage would be a suitable husband for Daridra as he would be busy in his meditation all day and would not be bothered  by her laziness. Krishna found a sage who was ready to marry Daridra. But after the marriage, the sage was so fed up with her laziness that he asked her to leave. Sadly, Daridra went to Laxmi asked Krishna to find  a suitable home for Daridra. Krishna found a peepal tree and asked Daridra to stay under it. Daridra asked Laxmi and Krishna to visit her, as she would get lonely. They promised to visit her on Saturdays. This is why people worship peepal trees on Saturdays because Krishna and Laxmi reside in them.