Responsa for Bava Batra 296:13

Q. A promised to give two marks for a holy cause should he cohabit with his wife, within the year. He did cohabit with her within that time. If such promise of a gift were made by an individual, even had such money been actually delivered to the donee, it would be considered an asmakhta and would be void. Therefore, this conditional promise for a holy cause should also be void, for, although a mere verbal promise for a holy cause is as valid as an actual delivery (of money and valuables) to a private person, it has no greater validity than such delivery; and any transaction classified as an asmakhta is invalid even if the money and valuables are actually delivered. Although a conditional promise classified as asmakhta, if accompanied by a kinyan and made before an authoritative court, is valid, its validity stems from the powers of confiscation inherent in the authoritative court, but not from an act of the promisor.
A. A must pay two marks to the holy cause. A mere verbal promise to a holy cause is as binding as a similar promise to an individual accompanied by any manner of conveyance that serves to validate such promise. Since a conditional promise classified as asmakhta is valid if accompanied by a kinyan and made before an authoritative court, a mere promise of this kind made to charity or to a holy cause is binding, even though the promise was not made before an authoritative court. The validity of a conditional promise made before an authoritative court does not stem from the court's power of confiscation, otherwise no kinyan would have been required. Moreover, the power of confiscation by a Jewish court is invoked only for the furtherance of proper conduct in accordance with Jewish principles (לפגדר מלתא) but not for the sake of validating private transactions.
This responsum was addressed to Rabbi Solomon "a prominent scholar from France".
SOURCES: Am II, 99; Mord. B.K. 44; cf. Cr. 299–300; Pr. 493; Agudah B.K. 51; Asher, Responsa 13, 2; Isserlein, Pesakim 53.

Q. While critically ill, Mrs. Maimona said to the representative of the community that after her death the following matters should be attended to at her expense: 1) That the oil-lamp which burns during the services in the memory of her departed daughter, should be made to burn continuously day and night; 2) that every Friday evening a half-pound waxen candle should be lit in the synagogue in her memory; and 3) that half a mark should be expended on a kiddush-cup for the synagogue. When the representative asked her as to the source of the money for these expenditures, she answered pointing at an adjoining room: "You will find sufficient valuables and money in that room." The following day, a Friday, she called her brother Zemah and told him, in the presence of witnesses, to take for himself and for his sisters everything he finds in the room mentioned above. On the following Sunday, the representatives of the community came and asked her the whereabouts of the money she promised for the synagogue, but she refused to reveal anything. The representatives, therefore, broke into the room and took everything they found there. They also pronounced the herem against anyone who would not return to the community valuables or money belonging to Mrs. M. which might be in his possession. R. Isaac ha-Kohen admitted that Mrs. M. had deposited eight Cologne-marks with him and had told him that after her death he should do with the money "the proper thing."
A. Mrs. M. probably withdrew her promise to donate something to the synagogue. A gift made causa mortis even to a holy cause can be rescinded. The money and valuables found in her room, therefore, belong half to R. Zemah and half to his sisters. R. Isaac must return the eight marks to Mrs. M's heirs, for the proper thing to do with money of a deceased person, is to return it to the heirs.
This Resp. is addressed to R. Jacob and the community of Linpurk.
SOURCES: Pr. 998: Mord. B. B. 624; Mordecai Hagadol, p. 326d; Agudah B. B. 202. Cf. Maharil, Responsa 75; Isserlein, Pesakim 73.