Riyad as-Salihin 1775
Anas bin Malik (May Allah be pleased with him) said:
The Messenger of Allah (ﷺ) forbade that a person in the city should make a deal on behalf of a villager on commission even if he is his real brother." [Al-Bukhari and Muslim]
عن أنس رضي الله عنه قال‏:‏ نهى رسول الله صلى الله عليه وسلم  أن يبيع حاضر لباد وإن كان أخاه لأبيه وأمه‏.‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏