Responsa על בבא קמא 227:3

Q. A claims that B took a valuable article of his, and, without his permission, gave it to a Gentile. B avers that the Gentile was A's creditor; that he had gone surety to the Gentile for A; and that he had to permit the Gentile to take A's article in order that he might free himself from this suretyship.
A. If B will take an oath in support of his claims, he will be free from obligation. Should A claim that he has paid his debt to the Gentile, such claim would be of no consequence. Since A did not repay the debt in B's presence, and since his creditor was a Gentile, who has held B directly responsible for such debt, and could still have collected it from B through the courts of the land, A was still under obligation to free B from his suretyship. Therefore, B acted within his rights.
SOURCES: Cr. 294.

Q. A consented to go surety for B to a burgher. The bishop and the judge released A from his suretyship, but the burgher refused to release him, and pressed him for money by threats and false accusations, until A was forced to make a money settlement with him. A, now, demands that B indemnify him for his loss.
A. B must indemnify A for all losses he suffered through his suretyship, even if the suretyship was used as a mere pretext for extortion. This is the law throughout our kingdom and is believed to be based on an ordinance of the communities. I believe, however, that it is sound talmudic law. But, A must prove the exact amount of his loss and can not collect by merely taking an oath. Even if witnesses testify that A gave a certain sum to the burgher and told him that the money was in final settlement of his suretyship for B, A must, nevertheless, swear that the money was given for that purpose only and that the burgher refused to accept a smaller amount in settlement of his claim. Only then may he collect that sum from B. If, however, A admits that the Gentile first released him from his suretyship and then returned with threats and accusations, B is free from any obligations to A.
SOURCES: Pr. 495; Mord. B. K. 160–161; Asher, Responsa, 18, 6. Cf. ibid. 18, 7; Agudah B. K. 138; Weil, Responsa 110; Moses Minz, Responsa 44; ibid. 74b.

Q. One quarter of a house belongs to A, and the other three quarters to B. A, needing money, negotiated a loan from a Gentile, who was willing to put up a mortgage of fifteen marks on A's part of the house on the following conditions: 1) That A pay the Gentile one mark per annum in perpetuity; 2) that in case A fails to pay the one mark per annum, the mortgaged part of the house is to belong to the Gentile; 3) that in case the house burns down, the ground shall be mortgaged to the Gentile on the same condition; and 4) that in case A wants to sell his part of the house, the Gentile is to have the privilege of buying it at twelve (?) marks less than the offer of the highest bidder. Before concluding this transaction, A informed B of his intentions and of the Gentile's terms, and offered to borrow the amount from B on the same terms. B vigorously protested against A's mortgaging part of the house to a Gentile who might cause B trouble; but, at the same time, he refused to lend fifteen marks to A on the ground that it would be considered a taxable loan, and that the one mark per annum would be considered usury from a fellow Jew.
A. If A sells his part of the house to B on condition that it be rented to A in perpetuity at one mark per annum, the sale will be legal and B will be permitted to collect the one mark per annum. If, however, B refuses to buy A's part on such terms, A may mortgage it to a Gentile.
SOURCES: Pr. 970.