Responsa על בבא בתרא 10:7

Q. A's widow and son, through their representative, summoned B, A's brother, before us. The representative claimed that A had given wine to B for the purpose of transporting it to Magdeburg and selling it there, and that B bartered this wine for a horse. He demanded, therefore, that B return the horse either to the widow, in payment of her ketubah, or to the orphan who was the rightful heir. B claimed that he had become surety to a Gentile for a loan of five and one quarter marks, contracted by A, that A's wife had vowed to repay this debt and release him from his suretyship; that A had given him the wine for the purpose of selling it and buying his release with that money; that the horse was worth only three marks, and that the widow, therefore, still owed him two and one quarter marks. The representative, however, claimed that A had effected B's release from his suretyship. We decided, temporarily, that B should take an oath to the effect that he has as yet not been released from his suretyship and that he had received the wine for the purpose of buying such release; in which case he should be entitled to retain the horse. However, before B took the prescribed oath, he sold the horse for six pounds, which now had a value of four and one-quarter marks, and he made a settlement with the Gentile (A's creditor for the 5¼ marks) to pay him one mark per year for six years. B wanted to give the six pounds to his mother-in-law for investment purposes, she promising to pay the one mark per year for six years to the Gentile. The representative, however, claimed that B was in possession of an amount equal to the value of the horse only and that B must pay out of his own pocket the difference between this amount and the amount due the Gentile. He demanded that B return the six pounds to the widow and her son, who were willing to provide sureties to the Gentile guaranteeing the payment of one mark per year for six years. B, on the other hand, claimed that he was entitled to benefit from the advantageous settlement he negotiated with A's creditor; that being able to release himself completely from his suretyship by his shrewdness in the use of the four and one-quarter marks, he was entitled to do so; and that he was taking a risk since (the coins comprising) the six pounds were almost certain to be invalidated and be worth less than four and one quarter marks. Moreover, B claimed that A had promised to pay him for his efforts in selling the wine, and that he had guaranteed another debt of A which had not been paid. We shall follow your decision in this matter. Furthermore, please inform us whether or not B may exact an oath from the widow to the effect that she did not vow to release him from his suretyship.
A. B has no claim on the money he received for the horse if his complete release from his suretyship is effected in other ways, especially since he had as yet not taken the required oath. Since the widow and her son are willing to guarantee such a release, B must return that money to them. However, if B take an oath to the effect that A owed him a certain amount of money, either for his effort in selling the wine or for becoming surety for another debt, he will be entitled to retain such an amount. B may exact an oath from the widow (to the effect that she did not vow to pay the above debt of five and one-quarter marks) under the following conditions only: a) If it is an established fact that A did not effect the release of B from his suretyship; b) if B claims that the widow had made the vow mentioned above before he became surety for A. If the former condition is lacking, the widow is not required to take an oath when the claim against her is based on a doubtful premise; and if the latter condition is lacking, the widow never became responsible for that debt. If she made the vow referred to above, she is still under solemn obligation to keep her vow, but is not required to take an oath. However, the representative's claim that B was in possession of an amount equal to the value of the horse only, is baseless.
SOURCES: L. 218, 219; cf. Hag. Maim., Shebuoth 11, 3.

Q. Prior to leaving for a large city, B said to A: "Buy six guldens from me, give me the price (in pennies) now and I shall give you the guldens upon my return from the trip." A agreed and paid over the money to B in the presence of one witness. B died while on the trip, and the community appointed a trustee for his property. A demands his money from the trustee.
A. On the order of the community, B's trustee should pay the six gulden to A. The latter is under no obligation to take an oath, in view of the fact that B died before the time for payment arrived.
SOURCES: Pr. 831.