Section 69(2) in The Transfer Of Property Act, 1882
(2)No such power shall be exercised unless and until—(a)notice in writing requiring payment of the principal money has been served on the mortgagor, or on one of several mortgagors, and default has been made in payment of the principal money, or of part thereof, for three months after such service; or(b)some interest under the mortgage amounting at least to five hundred rupees is in arrear and unpaid for three months after becoming due.
