Responsa for Bava Batra 200:9

Q. The bishop imprisoned B in order to extort money from him. B said to A: "You owe me eight marks, give five marks to the bishop". Meanwhile a rich Jew promised to speak to the bishop on B's behalf and assured B that he would thus effect his release. A, however, gave five marks to the bishop and B was released. Now B demands that A repay him the full eight marks.
A. A is under no obligation to repay the five marks to B since he carried out a direct order to pay this amount to the bishop. Moreover, had A acted on his own initiative and ransomed B without being requested to do so, he would still have been entitled to reimbursement, for a Jew should be ransomed even against his express will, and may be charged with the expenses thus incurred. The promise of the rich man to speak to the bishop was of no consequence, since he did not offer to spend money on B's behalf. We know that mere words are of no avail. The Gentiles are not moved by words, only money affects them. Those who fall into their hands have no hope for deliverance save through the payment of ransom.
This Responsum is addressed to Rabbi Haim Paltiel b. Jacob.
SOURCES: Cr. 32–3; Tesh. Maim. to Nezikin, 17. Cf. Maharil, Responsa 78.

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.