Is it permissible for an employee to accept a gift or money from companies he deals with, after receiving solemn oaths from them that it is merely a gift and not a bribe, and what should he do with the money if it is impossible to return it?

It is not permissible for an employee to accept gifts unless authorized by the employer. The gifts given to him are solely because he is an employee, and gifts to workers have been prohibited. It is obligatory to return the gift to its owner, or to give its value if returning it would cause offense, or to give it in charity on their behalf if the owner cannot be found.