The Book of Transactions (Kitab Al-Buyu`)
Muslim :: Book 10 : Hadith 3629
Ibn 'Abbas (Allah be pleased with them) reported Allah's Messenger (may peace be upon him) as saying: The riders (carrying merchandise) should not be met in the way, and townsman should not sell for a man of the desert. The narrator reported. I said to Ibn 'Abbas: What do these words really imply-" The townsman for the man of the desert"? He said: That he should work as a broker on his behalf.