Shevuot (Oaths) 36 - Oath of Deposit
If a person in possession of someone else's money - either a deposit, a loan, a stolen article, or the like - swears that he does not have it, he has taken what is known as an oath of deposit. If he swore falsely and subsequently confesses his sin, he must repay the principal plus an additional fifth and bring a "guilt offering" sacrifice in the Temple.
Although this oath applies to all types of debts - not just deposits - it is nevertheless called the "oath of the deposit", because a deposit is the first example mentioned in the Torah.
The oath of deposit applies to both men and women, to non-relatives and relatives, to those who are qualified to serve as witnesses, as well as to those who are disqualified, in court and out of court.
In truth, there is no reason to think that these rules would not apply - but they are only stated to contrast this with the oath of witnesses discussed previously.
Art: George Baxter - Stolen Pleasures