During the course of a search, the assessee admitted undisclosed income representing fictitious liabilities, unexplained money and unrecorded expenditure. The Assessing Officer levied a penalty under section 271AAB(1)(c), which the Commissioner (Appeals) reduced to 10 per cent under clause (a). The Tribunal held that although an additional legal ground challenging the levy of penalty was admissible under Rule 11 of the Income-tax (Appellate Tribunal) Rules, it had no merit. The assessee had failed to specify and substantiate the manner in which the undisclosed income had been derived, which is a mandatory requirement for claiming the concessional rate of penalty under section 271AAB(1)(a). Accordingly, the order of the Commissioner (Appeals) reducing the penalty was set aside, and the penalty levied by the Assessing Officer under section 271AAB(1)(c) at 30 per cent was restored. (AY. 2016-17)