Bava Metzia 42 - Negligence of Unpaid Custodian
If one deposited money with another for safekeeping - who then either bundled it up in a kerchief and slung it behind him or gave it over to his young son or daughter, but did not adequately lock the door before them - the custodian is liable for loss and damage, because he did not guard the money in the normal manner of custodians.
A custodian put money in a hunter's ambush hut, which provides adequate protection against theft, but not against fire. In the end the money was stolen. The situation began with negligence but ended with an unavoidable mishap - and he is liable.