I saw and information somewhere that Einstein was working at patent bureau and stole a work of some mathematician (relativity theory probably). Are there any proof?
He did work in a patent bureau.
He did not steal his achievements there: Theoretical physics is published in journals, not patented.
For sure not the whole structure of General and Special Relativity was his brainchild alone. There were others who worked on related ideas before him (Poincare, Lorentz), and there were those who helped him with the math (Hilbert, Minkowski)
And it seems that he worked closely with his wife and often failed to credit her properly.
Nevertheless, much was undoubtedly original in Einstein's work.