The Indian Evidence Act, 1872
Chapter 02 Of the Relevancy of Facts
Section 44: Fraud or collusion in obtaining judgment, or incompetency of Court, may be proved
Any party to a suit or other proceeding may show that any judgment, order or decree which is relevant under sections 40, 41 or 42 and which has been proved by the adverse party, was delivered by a Court not competent to deliver it, or was obtained by fraud or collusion.