Sahih Bukhari | Volume 3 | Hadith Number 474

Narrated by Tawus
Ibn 'Abbas said, "The Prophet forbade the meeting of caravans (on the way) and ordained that no townsman is permitted to sell things on behalf of a bedouin." I asked Ibn 'Abbas, "What is the meaning of his saying, 'No townsman is permitted to sell things on behalf of a bedouin.' " He replied, "He should not work as a broker for him."