We were forbidden for a town-dweller to sell on behalf of a desert-dweller, even if he were his brother or his father.
أخبرنا محمد بن المثنى قال حدثني سالم بن نوح قال أنبأنا يونس عن محمد بن سيرين
نهينا أن يبيع حاضر لباد وإن كان أخاه أو أباه
Muslim narrated it in Buyu, chapter titled "The prohibition of a city dweller selling on behalf of a bedouin," Hadith: 21/1523, from the report of Yunus bin Ubayd. Bukhari narrated it in Buyu, chapter titled "A city dweller buying for a bedouin as a broker," Hadith: 2161, from the report of Muhammad bin Sirin, with the same wording. It is also found in Al-Kubra, Hadith: 6084.