Sa’if 11, Mechaber: A person makes a voluntary statement to another that he owes him a maneh. The other responds and says he is certain he is not owed anything. The person who made the voluntary statement is exempt from paying anything. This is so even though even if he is certain that he does owe the maneh, because it is as if the other forgave the debt.
Ner Eyal: The person who responds that he is owed nothing must say he is “certain” he is owed nothing. Otherwise his statement will not be deemed a forgiveness of the loan. Generally, a person who is not facing a claim cannot create an obligation for himself by simply volunteering an admission that he owes money. Similarly, one cannot forgive an obligation of another towards oneself by simply saying that the obligation does not exist.
In order for an admission of a debt or for the forgiveness of a debt to be effective, it must be accompanied by some overt manifestation of serious intent. Such overt manifestation may take the form of a statement in front of witnesses that one owes another person money, or that one has forgiven the debt. It may take the form of a document in which one makes a written statement to that effect which one signs. Such a declaration before witnesses or statement in writing is binding, even though everybody involved knows it is not true.
Just like a guarantor can assume an obligation that was not his, so too can a person create an obligation for himself or forgive a debt of another, even though he was not obliged to do so. But it must be done unambiguously, either in front of witnesses or in a signed declaration.
In the case under consideration in this Sa’if 11, although the forgiveness of the loan is not done in front of witnesses or in a signed declaration, it is nevertheless effective because the person forgiving the loan has used assertive language, he is “certain” that he is owed nothing. Were he not to use the word “certain,” the loan would not be effectively forgiven.