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] (ID)
App reference (ID): Book 18, Hadith 265 (ID)
Arabic/English book reference (ID): Book 18, Hadith 1775 (ID)