Indian Contract Act, 1872
216. Principal's right to benefit gained by agent dealing on his own account in business of agency
If an agent, without the knowledge of his principal, deals in the business of the agency on his own account instead of on account to his principal, the principal is entitled to claim from the agent any benefit which may have resulted to him from the transaction.
A directs B, his agent, to buy a certain house for him. B tells A it cannot be bought, and buys the house for himself. A may, on discovering that B has bought the house, compels him to sell it to A at the price he gave for it.