If the owner of an object claims: "I lent it to you," "I rented it to you," or "I entrusted it to you," and the defendant responds: "This never took place," or "That is true, but I returned it to you, and my responsibility was concluded. There is no obligation between us at all," the defendant must take a sh'vuat hesset. He is then freed of responsibility.
When does this apply? When the watchman's responsibility is not recorded in a legal document. If, however, a legal document recorded that the article was entrusted, rented or lent, and the watchman claims that he returned the article, he must affirm his statement with an oath taken while holding a sacred article. The rationale for this ruling is that since an unpaid watchman could claim that the article was stolen or lost, and a borrower could claim that it died because he was working with it, his word is accepted when he says he returned it. But just as if he claimed that it was destroyed by forces beyond his control, he would have been required to take a Scriptural oath while holding a sacred article; so, too, when he claims to have returned it, he is required to take an oath resembling a Scriptural oath. The rationale is that the plaintiff has a legal document recording that the article was entrusted.
When does the above apply? When the watchman could have claimed that the article was destroyed by forces beyond his control without having to bring proof of his claim. If, however, he would have to bring proof of his claim, as will be explained, his word is not accepted if he claims that he returned the article. Instead, the plaintiff in possession of the legal document should take an oath while holding a sacred article that the watchman did not return anything to him. The watchman is then required to make restitution.
There is no other instance where a defendant is obligated to take an oath while holding a sacred article because he could have used another argument, except a watchman against whom a legal document serves as evidence. Whenever any other defendant is obligated an opportunity to take an oath, because he could have used another argument, all that is involved is a sh'vuat hesset.