Responsa על בבא בתרא 247:3

Q. A and his brothers were arrested by the bishop. They subsequently agreed to pay him a ransom of two thousand [white denarii?]. The brothers agreed among themselves that each one contribute an equal amount to the payment of the ransom. A, however, was short five hundred "white denarii" [and his brothers had to make up the difference]. Subsequently the bishop agreed to reduce the payment by five hundred [white denarii?]. A demands his share of the reduction.
A. Each brother is entitled to a share in the reduction proportionate to the amount he has paid.
SOURCES: Cr. 307.