The Messenger of Allah ﷺ said, "Do not go out to meet the caravans in order to buy from them. Do not undercut one another's sales. Do not artificially inflate prices. A town-dweller must not sell on behalf of a desert-dweller. Do not leave camels and sheep unmilked to make their udders appear full. Whoever buys such an animal has, after milking it, the better of two choices. If he is pleased with it, he may keep it, and if he is displeased, he may return it along with a measure of dates."
أن رسول الله ﷺ قال: لا تلقوا الركبان للبيع، ولا يبغ بعضكم على بيع بعض، ولا تناجشوا، ولا يبغ حاضر لباد، ولا تصروا الإبل والغنم، فمن ابتاعها بعد ذلك فهو بخير النظرين بعد أن يحلبها: إن رضيها، أمسكها، وإن سخطها ردها وصاعا من تمر.
Malik narrated it in the Book of Sales (96) from Abu Zinad, from Aaraj, from Abu Hurairah, and he related it.Bukhari narrated it in the Book of Sales (2150), and Muslim in the Book of Sales (1515:11), both of them through the route of Malik, with the same wording.Muslim also narrated it (1524:28) through the route of Hammam bin Munabbih, who said, "This is what Abu Hurairah related to us from the Messenger of Allah ﷺ," and he mentioned several hadiths, among them, "If any of you buys a lakhah with tied-up udders or a sheep with tied-up udders, he has the choice, after milking it, either to keep it or to return it along with a saa of dates."