Sahih Bukhari
Sales and Trade
Volume: 003 / Book Number: 034 / Hadith Number: 367
Narrated Tawus:
Ibn 'Abbas said, "Allah's Apostle said, 'Do not go to meet the caravans on the way (for buying their goods without letting them know the market price); a town dweller should not sell the goods of a desert dweller on behalf of the latter.' I asked Ibn 'Abbas, 'What does he mean by not selling the goods of a desert dweller by a town dweller?' He said, 'He should not become his broker.' "