عن أنس رضي الله عنه
قال: نهى رسول الله صلى الله عليه وسلم: أن يبيع حاضر لباد وإن كان أخاه لأبيه وأمه
The Messenger of Allah (sallallahu alayhi wa sallam) 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.
Riyad as-Salihin 1775, Book 18, The Book of the Prohibited actions, Hadith 265. 1 min read