A handed over his watch to B for safe-keeping, B sells the watch to C, which he was not authorised to do, B is prosecuted for theft.
B has not committed theft. Since, theft is committed when an immovable property is taken dishonestly from the possession of any person without his consent.
As per the facts, even though A was the owner of the watch but he had transferred the possession of the watch to B for safe keeping and therefore the person whose consent to move the watch was required is B himself. Since he had the possession of A's watch. Therefore, B has not committed theft.