The Prophet ﷺ said, "Do not go out to meet riders coming with goods to buy from them before they reach the market, and do not tie up the udders of camels and sheep to make them appear full of milk. Whoever buys such an animal has the better of two choices after milking it. If he wishes, he may keep it, and if he wishes, he may return it along with a saa of dates."
أخبرنا محمد بن منصور قال حدثنا سفيان عن أبي الزناد عن الأعرج
عن النبي ﷺ قال لا تلقوا الركبان للبيع ولا تصروا الإبل والغنم من ابتاع من ذلك شيئا فهو بخير النظرين فإن شاء أمسكها وإن شاء أن يردها ردها ومعها صاع تمر
Its chain of transmission is sahih. Ahmad narrated it in 2/242, 243, from Sufyan bin Uyayna, with the same chain, and he clarified that he heard it directly. It is also in Kubra, hadith 6079, and it is agreed upon, narrated by Bukhari, hadith 2150, and Muslim, hadith 11/1515, from the hadith of Malik, from Abu Zinad, with the same chain.