If you are wondering where to link to the original source in an article then do so at the beginning of the article instead of pointing it at the bottom. This is although the personal opinion of Matt Cutts. In true sense, it does not really matters if you point to the original source at the beginning of the article or at the bottom. The Page Rank would be passed in both the cases. But yes, linking to the source at the beginning is always better from user point of view.
Have a look at this video where Matt answers the question –
“If I write about another article, where should I link to the original source?” asked by Nayan Seth of India.