Now as a man is like this or like that,

according as he acts and according as he behaves, so will he be;
a man of good acts will become good, a man of bad acts, bad;
he becomes pure by pure deeds, bad by bad deeds;

And here they say that a person consists of desires,
and as is his desire, so is his will;
and as is his will, so is his deed;
and whatever deed he does, that he will reap.

Brihadaranyaka Upanishad 4.4.5-6

Thanks for the great article. Source: http://www.collective-evolution.com/2015/12/13/a-truth-about-karma-that-you-wont-hear-from-the-mainstream-version/