Section 142(7)(a) in The Central Goods and Services Tax Act, 2017
(a)every proceeding of appeal, review or reference relating to any output duty or tax liability initiated whether before, on or after the appointed day under the existing law, shall be disposed of in accordance with the provisions of the existing law, and if any amount becomes recoverable as a result of such appeal, review or reference, the same shall, unless recovered under the existing law, be recovered as an arrear of duty or tax under this Act and the amount so recovered shall not be admissible as input tax credit under this Act.