law: Transfer of Property Act, 1882
  25. Conditional transfer
  An interest created on a transfer of property and dependent upon
  
  a condition fails if the fulfillment of the condition is impossible, or is
  
  forbidden by law, or is of such a nature that, if permitted, it would defeat
  
  the provisions of any law, or is fraudulent, or involves or implies injury to
  
  the person or property of another, or the court regards it as immoral or
  
  opposed to public policy.
  Illustrations
  (a) A lets a farm to B on condition that he shall walk a hundred
  
  miles in an hour. The lease is void.
  (b) A gives Rs. 500 to B on condition that he shall marry A's
  
  daughter C. At the date of the transfer C was dead. The transfer is void.
  (c) A transfers Rs. 500 to B on condition that she shall murder
  
  C. The transfer is void.
  (d) A transfers Rs. 500 to his niece C, if she will desert her
  
  husband. The transfer is void.