Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Do not go out to meet the trade caravans outside the town; no one should strike a deal over another's deal; do not (deceptively) inflate prices; no town-dweller should sell for a desert-dweller; and do not sell camels and goats with milk withheld in their udders. If anyone buys such an animal (whose milk has not been drawn for several milkings), then after milking it he may choose whichever of the two options he wishes: if he is pleased with the animal he keeps it; otherwise he returns the animal along with a sa' of dates."
(b) Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) forbade "that a Muhajir should sell for a Bedouin."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10901