Responsa על בבא מציעא 73:11

Q. A says that B's mother before her death instructed B to give A one Mina out of her possessions, since she had owed money to A's mother and did not remember whether or not she had repaid the entire sum. B denies having received such instructions from his mother, and further claims that A's mother owed him more than one Mina. But A has witnesses who testify that after his mother's death B admitted having received these instructions.
A. Since B's mother did not take the required oath regarding her ketubah, she had no property of her own; even the clothes she wore on week-days belonged to the estate. Consequently B is unable to carry out his mother's instructions. B is under no moral obligation to repay his mother's debt since the mother herself had not been pressed for payment.
SOURCES: Cr. 76.