Where do Reserve Bank of India’s surplus funds come from?

Reserves with RBI are not all of the same kind. In the current debate, there are two which are relevant: The Currency & Gold Revaluation Account (CGRA) and the Contingency Fund (CF). The CGRA and CF put together constituted 26% of assets (and because in a balance sheet assets and liabilities must by definition match, also the same proportion of its liabilities).