Bhagavad Ghita about prayer

I read a very interesting story today.
The blog where I found it is in russian
but the link to the sourse says, the story comes from Bhagavad Ghita. (in german)
(The site I post here and other sites about buddhismus you can find in My Interests Site)
Unfortunately I had no time to read all this text. But one day I'll do it.
Now, to the story.

One man tryed to pray for many years but had no effect. So decided to visit an important master. Went to him and ask him to explain the situation.
The monk said
-Take that very dirty sieve and bring me water.
The man went to the river but could not bring water. Come to the monk and said him about it.
-Try again, repeat the monk.
The man went to the river second time but could not bring water.
-Patience. Try again.
Nothing.
-It's unpossible to bring water with the sieve, said the man to the monk.
-You are right, answered the wise man, it's unpossible to bring water,but the sieve was dirty first and now it's clean.