Responsa for Bava Metzia 3:5

Q. In the presence of witnesses, A gave merchandise to B on credit. When the time for payment arrived, A claimed that B owed him twenty-five shillings, but B claimed that the amount due was twenty-four shillings. The witnesses supported B's claim, but A claimed that they were mistaken, and demanded that either B take an oath and pay twenty-four shillings or else he, A, would take an oath and collect twenty-five shillings.
A. Since witnesses support B's claim, he is under no obligation to take an oath.
SOURCES: Pr. 829.