Musnad Ahmad 30:3518

Aswad ibn Amir narrated to us, Abu Bakr informed us, from Asim, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not outbid one another (to deceive), do not turn your backs on one another, do not compete (in worldly matters), do not envy one another, and do not hate one another. Let no man outbid the bid of his brother, and let no city dweller sell for a desert dweller. Leave the people, for Allah provides for some of them through others. And let no woman stipulate the divorce of her sister (co-wife)."