Responsa for Shevuot 86:3

Q - A wanted to borrow money from B but the latter refused to lend A any money whatsoever, unless A would deposit a pledge with a third party chosen by B. C was designated by B, to act as the third party. B, thereupon, lent A the money, only after having learned that the pledge was already in C's possession. The pledge was destroyed in a conflagration. A claims that B should bear the responsibility for the loss of the pledge, since B had insisted that the pledge be placed in C's possession.
A - B is not held responsible for the loss of the pledge, even if C was found to be guilty of negligence, since A had personally given the pledge to C.