Responsa for Shevuot 81:10

Q. B gave A two marks to invest and, from the profits, to pay every year a certain amount to charity to commemorate the soul of his departed wife. Now B demands that A pay him back the principal plus the accrued interest. A, however, claims that he received the two marks from B in order to give it, together with the interest, to any charity he pleases. He, therefore, refuses to return the money to B.
A. If B admits that the principal was also meant for charity, but claims that he wants to distribute it himself, A is free from any obligation to B, and is not even required to take an oath, since no actual money loss to B is involved.
SOURCES: Cr. 87; Pr. 286; Mord. Shebu. 767.

Q. A demands that Leah return to him the money he deposited with her. Leah claims that A deposited the money with her on condition that she do not return it to him without his wife's consent. [A's wife does not consent to the return of the deposit]. Are we to believe a trustee who was appointed by the two opposing parties regarding the terms of his trusteeship, or may we require him to take an oath? Moreover, Leah is a married woman. May her husband object to her being degraded by imposing an oath on her?
A. A trustee appointed by both parties is not required to take an oath regarding the terms of his trusteeship. But, Leah was not appointed trustee by both parties. She was only appointed by the husband, and, therefore, is required to take an oath. Leah's husband cannot object to imposing an oath on her. If the law requires that a woman take an oath, the husband has no right to protest against her being degraded in court. But, since Leah, as long as she is married, has no money of her own, and were she to claim that she had already returned the deposit, no oath would be imposed on her, we now lend credence to her words and require no oath. However, the court should give A a writ stating that after Leah will be divorced or widowed she will have to return the money to A or take an oath to the effect that A deposited the money with her on condition that she return it upon his wife's consent only.
SOURCES: L. 306–7; Mord. B. K. 89. Cf. Pr. 739; Tesh. Maim. to Mishpatim, 44.

Q. A claims he has no cash and wants to repay his debt to B with goods. B demands that A swear that he has no cash. Is it not true that the court can not require an oath from A since no actual loss of money to B is involved?
A. The fact that there is no actual loss of money to B does not, of itself, absolve A from taking an oath. A is not required to take the oath for another reason. B can not claim to be certain that A has cash, and no one is required to take an oath when his opponent is not certain of his claim.
This Responsum is addressed to Rabbi Asher b. Moses.
SOURCES: Cr. 7, 8; Pr. 109; L. 360. Cf. Am II, 224.