I was in need of a loan of $5,000. Shimon agreed to lend me $3,000; Levi agreed to lend me $2,000. I put all of the money in my wallet. When I later counted the money, I had $5,100. I have no way of knowing who gave me the extra $100. When I contacted Shimon and Levi, neither of them knew whether they had given me the extra cash.

Q: Am I obligated to return the money, and if so, to whom?

A: At first glance, it seems that this answer is resolved based on a clear precedent in halacha. Shulchan Aruch (76:1, 300:1) discusses the case of two people who separately deposit money by Reuven, one person $100 and the other $200. Later, Reuven does not recall who deposited the $200, and each depositor claims that he is the one. The halacha is that each claimant must take an oath that he deposited $200, and Reuven is then obligated to pay each of them $200. Since Reuven was not careful to keep track of the money, he ends up losing $100. In the event that the depositors themselves do not recall how much they deposited, although it is clear that neither is lying, Reuven is not responsible to pay each of them the full amount since neither has a definite claim against him (Nesivos 76:9). Therefore, Reuven should split the money in question and give half to each of them (Shach 76:7, 13, see also Ketzos 365:1, 138:1). If he wants to be sure that he fulfilled his obligations latzes yedei shamayim (a non-enforceable halachic obligation), he should give each depositor $200. The reason that he is responsible latzes yedei shamayim is because of his negligence. He should have been concerned that such an issue could arise and kept an exact record when he received the money.

However, since a mistake such as yours is uncommon, you were not expected to examine the amount. As such, not counting the money upon receipt was not negligent, so you are not liable latzes yedei shamayim. This is similar to the halacha (C.M. 300:1) that rules that if two parties deposited monies with one guardian, he is not responsible to pay the full amount to both. But, as previously mentioned, he would split the extra money between the two.

Upon further consideration, the above analysis is not the correct address to resolve your inquiry. Your situation is not a case of a custodian or borrower who did not properly care for the money that was given to him. Your situation involves lost money that ended up in your possession. When one of the two lenders mistakenly gave you an extra $100, he essentially lost that money. Since it entered your possession before the owner realized that it was lost (before yei’ush [despair]) you are responsible to return it to the owner in the same way as when finding any other lost object.

Since there is no way for you to know which of the two lenders “lost” the money, you are obligated to keep possession of it until there is clarification to whom the money should be returned. If they come to an agreement as to what to do with the money, you are required to return it accordingly (see C.M. 267:8). [However, up to that point you may use the money (see Hashovas Aveida KeHalacha 6:3)].