Sahih al-Bukhari 2727

It is related that Abu Hurayra said, "The Prophet, may Allah bless him and grant him peace, forbade meeting caravans, a Muhajir selling on behalf of a man of the desert, a woman making a precondition of the divorce of her sister, a man overbidding the sale of his brother, and he forbade bidding against one another to raise the price and also leaving animals unmilked [for days to make it appear that the animal has a lot of milk]." It was corroborated by Mu'adh and 'Abdu's-Samad from Shu'ba. Ghundar and 'Abdu'r-Rahman said, "It is prohibited (passive tense)." Adam said, "We were forbidden." An-Nadr and Hajjaj ibn Minhal said, "He forbade."