There is a fine story of a poor old lady who was selling some fruit she had gathered in order to make ends meet.
As she walked back and forth on the streets calling people to come and buy, the child Krishna, disguised as a beggar boy, walked up to her asking to eat some fruit from her basket.
She was a kind one and though it would cost her, she didn't refuse him. The child ate every one, thanked her and left!
As she wondered about her loss, she looked down at her empty basket to find it was filled with jewels.
So it is that when you give selflessly to Krishna [or to something truly worthwhile], you are returned a thousandfold!
Source: Pictures from Mystics by T.L. Vaswani
Here is another version of this famous story.