Section 122
Estoppel against denying signature or capacity of prior party
Chapter 13: Special rules of evidence
No indorser of a negotiable instrument shall, in a suit thereon by a subsequent holder, be permitted to deny the signature or capacity to contract of any prior party to the instrument.
The Negotiable Instruments Act, 1881 (Act No. 26 of 1881). From the updated text on India Code, with later amendments. Being checked against the official copy; amendment notes are not shown yet.