Where in any financial year an assessee has incurred any expenditure and he offers no explanation about the source of such expenditure or part thereof, or the explanation, if any, offered by him is not, in the opinion of the Assessing Officer, satisfactory, the amount covered by such expenditure or part thereof, as the case may be, may be deemed to be the income of the assessee for such financial year :

Provided that, notwithstanding anything contained in any other provision of this Act, such unexplained expenditure which is deemed to be the income of the assessee shall not be allowed as a deduction under any head of income.