Section 19 of the Indian Evidence Act, 1872
A undertakes to collect rents for B.
B sues A for not collecting rent due from C to B
A denies that rent was due from C to B
A statement by C that he owed B rent is an admission, and is a relevant fact as against A, if A denies that C did owe rent to B.
Section 19 and Section 20 are exceptions to the general rule laid down in Section 18. Under this section the parties to the proceeding may use the statement of third person if the statement of third person contained an admission against his own interest, and could have been used against him if he sued or was sued in connection with matter involving the position or liability affected by that admission.
In other words, “the admission of a third person against his interest, when it affects his position or liability and when that position or liability has to be proved against a party to the suit, is relevant against the party.” The admissibility of statement made by a third person depends upon the proof of his position as against the parties to the suit or proceeding. An admission by the third person is relevant only upto his liability.