Sahih al-Bukhari 2163
Sahih al-Bukhari · Book 34: Sales and Trade · It is forbidden to meet the caravans on the way (to buy the goods away from the market)
Narrated Tawus:
حَدَّثَنِي عَيَّاشُ بْنُ الْوَلِيدِ ، حَدَّثَنَا عَبْدُ الأَعْلَى ، حَدَّثَنَا مَعْمَرٌ ، عَنِ ابْنِ طَاوُسٍ ، عَنْ أَبِيهِ ، قَالَ سَأَلْتُ ابْنَ عَبَّاسٍ ـ رضى الله عنهما ـ مَا مَعْنَى قَوْلِهِ " لاَ يَبِيعَنَّ حَاضِرٌ لِبَادٍ ". فَقَالَ لاَ يَكُنْ لَهُ سِمْسَارًا .
I asked Ibn `Abbas, "What is the meaning of, 'No town dweller should sell (or buy) for a desert dweller'?" Ibn `Abbas said, "It means he should not become his broker."