Musnad Ahmad 30:1999

Abu Ahmad narrated to us, he said: Kathir ibn Zayd narrated to us, from al-Walid ibn Rabah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not hate one another, do not envy one another, do not outbid one another (to deceive), and do not turn your backs on one another. And be, O servants of Allah, brothers." "Let no resident sell for a bedouin, do not meet the caravans (to buy from them before they reach the market), and whoever buys a sheep and finds it to have been withheld from milking (to deceive the buyer), let him return it, and return with it a sa' of dates." "Let none of you outbid the bid of his brother, do not propose to a woman to whom your brother has proposed, and let no woman ask for the divorce of her sister (in faith) so that she may empty her vessel (take her place), for her provision is upon Allah, the Almighty and Majestic."