125. Where, in the course of any proceeding in connection with the assessment of tax under Chapter IX, the Deputy Commissioner of Taxes is satisfied that any person has- (a) without reasonable cause, failed to pay advance tax as required by section 64; or (b) furnished under section 67 any estimate of tax payable by him which he knew, or had reason to believe, to be untrue, he may impose upon such person a penalty of a sum not exceeding the amount by which the tax actually paid by him falls short of the amount that should have been paid.