Responsa על בבא בתרא 84:2

Q. A and B were captured and held for ransom. The former was rich and the latter, poor. A spent money with the help of his mother and effected the release of both A and B. A claims that B asked to be ransomed, and therefore demands that B pay his share of the expenses. B denies having asked to be ransomed.
A. A Jew should be ransomed even against his express will, and be charged with the expenses incurred. A captive in the hands of Gentiles is exposed to ruthless treatment and incessant flogging, and his very life is in danger. Therefore, anyone who effects the ransom of a Jew is praiseworthy and is entitled to the expenses incurred. Moreover, Jews threatened by a common danger may force one another to contribute of their means to the measures that will free them of that danger. A and B have to share the expenses in proportion to their wealth, since they were captured for the purpose of extorting money from them.
R. Meir adds that this question had already been sent to him from Magdeburg. He had also been asked concerning a tutor who was arrested because of a false accusation, and who requested his former employer not to ransom him. R. Meir's answer was the same.
SOURCES: Pr. 39; L. 345, cf. Mord. B. K. 58–59; Cr. 32–33; Am. II, 128; Tesh-Maim. Nezikin, 17. Weil, Responsa 148; ibid. 149; Moses Minz, Responsa 1.

Q. A, B, and Leah, jointly lent 108 pounds to a Gentile. When the latter came to repay part of his debt in wine, as he used to do in former years, A and Leah, in B's presence, offered to take five wagons of wine at six pounds per wagon, which offer the Gentile rejected. Subsequently the Gentile met A's son, C, and complained to him about the ill treatment he received at the hands of his creditors. He also told the people in the street, that A, B, and Leah had already collected from him a thousand pounds in interest. To appease him, C agreed to take six wagons of wine for thirty-seven pounds. When A and Leah heard of it, they consented to take the wine, and ordered its delivery. Now, B refuses to accept his part of the wine claiming that he did not consent to the bargain, and that he would seek to collect cash from the Gentile. A claims that B angered the Gentile, who, consequently, repaid almost the entire debt, and thus caused them a considerable loss of money.
A. Whatever one partner does is binding on all other partners unless they openly protest against that partner's acts. Since B did not protest at the time of the first negotiations, he is bound by the subsequent agreement.
SOURCES: Pr. 961.