Musnad Ahmad 30:2187

Muhammad ibn Ja‘far narrated to us, he said: Shu‘bah narrated to us, from al-Mughirah, from Ibrahim, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), that he said: "Do not tie up the udders of camels and sheep. Whoever buys a tied-udder animal has the choice of two options: if he wishes, he may return it and return with it a *sa‘* of dates." He said: "And a man should not undersell the sale of his brother, and a woman should not ask for the divorce of her sister in order to empty her plate, for she only has what is written for her. And do not practice *najash* (bidding up prices without the intent to buy), and do not meet the caravans (for trade before they reach the market)."