If one finds someone’s lost object he must return it and
not accept a reward for doing so. However, a reward may be
accepted if it is appreciation for something ancillary to the actual
lost object. For example, the Chazon Ish held that notifying the
owner that you found it and have it, is sufficient. One could
accept a reward for then delivering it. (úùåáåú åäðäîåú 3:463)