Validity of acknowledging a debt to a fetus when the stated reason for the debt is invalid?

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If a person acknowledges a debt to the fetus and attributes it to an invalid cause, such as a loan or a deposit that the fetus allegedly provided, the acknowledgment is void according to the view of At-Tamimi. However, according to the view of Ibn Hamid, the acknowledgment should be valid, as connecting the acknowledgment to something that invalidates the debt results in the nullification of the connector, similar to stating, 'I owe a thousand, but it is not obligatory upon me.'