Question: I went to pray at the Kotel and found a $100 bill between the stones. Am I allowed to take it?

Answer: This is a great question. It depends on the person who put the money there. If they intended to dedicate it to the Beit HaMikdash, then it is forbidden to benefit from it, as stated by the Rambam (Matanot Aniyim 8:8). However, it seems that in most cases, people who leave money there do so with the hope that someone in need will take it, as a form of tzedakah. Therefore, it’s permissible to take it, especially if the person is in need. See Shut Mishnat Yosef (Vol. 11, Siman 204) that if the person who finds the money is poor, he may take it for himself. If he isn’t in need, the right thing to do is to donate it to the Kotel’s charity fund located at the entrance.