120. No maker of a promissory note, and no drawer of a bill of exchange or cheque, and no acceptor of a bill of exchange for the honour of the drawer shall, in a suit thereon by a holder in due course, be permitted to deny the validity of the instrument as originally made or drawn.
Negotiable Instruments Act, 1881
Section 120: Estoppel against denying original validity of instrument
Chapter XIII — Special Rules of Evidence
Source: official text of the Negotiable Instruments Act, 1881.