I heard/red that sentence thousands of times, but never heard for source of such claims. I mean, there must be some chronicle, charter, whatever. But there is nothing. Next, time please, try to provide source.

It was an accomplishment back in those days. Tsar Dushan stated that as a victorious act, therefore it was mentioned in his chronicles. I don't have access to an archive where I could find that chronicle, but it is there.

I dont really wish to go in it. From my experience it is just new age with Slavic flavour. (sometimes with lot of Dharmic influences)

As I have already stated, it can get pretty dumb, so to say, if the pseudo-historians practice it. The true followers of that religion and tradition take their sources from folklore and customs that can be found in more conservative Slavic areas.