Is it permissible for an employee to keep the remainder of the amount disbursed to him for lodging and food allowance during a work assignment, after reducing his expenses?

The reference for determining the ruling on disposing of money paid by an employer for sustenance and travel expenses is the nature of this payment. If it is a grant of ownership to the employee, then he may economize the amount and keep some of it. However, if it is in exchange for actual expenses incurred, then he is only entitled to what he genuinely spent, and he must return the surplus.