Language:
كتاب البيوع
34  
Sales and Trade
(68)
Chapter: Is it permissible for a person from the town to sell the goods of a desert dweller
(68)
بَابُ هَلْ يَبِيعُ حَاضِرٌ لِبَادٍ بِغَيْرِ أَجْرٍ وَهَلْ يُعِينُهُ أَوْ يَنْصَحُهُ
Sahih al-Bukhari 2158

Narrated Tawus:

Ibn `Abbas said, "Allah's Messenger (ﷺ) 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.' "

حَدَّثَنَا الصَّلْتُ بْنُ مُحَمَّدٍ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، حَدَّثَنَا مَعْمَرٌ، عَنْ عَبْدِ اللَّهِ بْنِ طَاوُسٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ لاَ تَلَقَّوُا الرُّكْبَانَ وَلاَ يَبِيعُ حَاضِرٌ لِبَادٍ ‏"‏‏.‏ قَالَ فَقُلْتُ لاِبْنِ عَبَّاسٍ مَا قَوْلُهُ لاَ يَبِيعُ حَاضِرٌ لِبَادٍ قَالَ لاَ يَكُونُ لَهُ سِمْسَارًا‏.‏
Reference : Sahih al-Bukhari 2158
In-book reference : Book 34, Hadith 109
USC-MSA web (English) reference : Vol. 3, Book 34, Hadith 367
  (deprecated numbering scheme)