Musnad Ahmad 30:2330

Muhammad ibn Fudayl narrated to us, from Mughirah, from Ibrahim, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not tie up the udders of camels and sheep (to deceive buyers). Whoever buys a tied-udder animal has the choice of two options: if he wishes, he may keep it, and if he wishes, he may return it along with a sa' of dates. A woman should not ask for the divorce of her sister (to take her place), do not engage in Najash (bidding up the price without the intention to buy), do not sell over the sale of one another, and a city dweller should not sell for a bedouin."