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