Musannaf Ibn Abi Shayba 26:567

Abu Usama narrated to us, from Sulayman ibn al-Mughirah, who said: I asked al-Hasan about a man who had a transaction with a woman from the people of the dhimma (protected non-Muslims), and she had something of his, and he cast her off (or abandoned the matter), and he did not find her. Should he place it in the public treasury (Bayt al-Mal) of the Muslims? He said: Yes.