Is it permissible for a property owner who manages a real estate office to take a commission for selling a property that belongs to him?

The commission taken by the real estate agent for guiding a buyer falls under the category of ju'alah (a promised reward for a specific task). Scholars have differed regarding the permissibility of combining ju'alah with a sale in a single contract. Some have held that it is impermissible, while others have allowed it. The latter opinion is the more sound, as there is no prohibition in combining them with a sale in one contract, and because each of them is permissible individually.