law: Indian Evidence Act, 1872 
  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 section 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.