Compiled by Imam Yahya ibn Sharaf al-Nawawi
عن أنس رضي الله عنه قال: نهى رسول الله صلى الله عليه وسلم أن يبيع حاضر لباد وإن كان أخاه لأبيه وأمه. ((متفق عليه)).
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]