Riyad as-Salihin, Book 18, Hadith 1777 (In-Book) ⓘ

Ibn 'Abbas (May Allah be pleased with them) said: The Messenger of Allah said, "The caravans carrying merchandise should not be met on the way to purchase from them; a man in the city should not sell for a man of the desert."Tawus asked him (Ibn 'Abbas): "What do these words really imply?" He said: "He should not work as an agent on his behalf."[Al-Bukhari and Muslim].

وعن ابن عباس رضي الله عنهما قال‏:‏ قال رسول الله صلى الله عليه وسلم ‏:‏ “لا تتلقوا الركبان، ولا يبع حاضر لباد‏"‏ فقال له طاوس‏:‏ ما قوله‏:‏ لا بيع حاضر لباد‏؟‏ قال‏:‏ لا يكون له سمسارًا‏.‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏