The Messenger of Allah ﷺ said, "Whoever sells an animal whose milk has been left to gather in the udder to make it look more productive, the buyer has the right of choice for three days. If he wishes, he may return it, along with a measure of dates."
ومن باع مصراة فالمشتري بالخيار ثلاثة أيام إن شاء ردها ورد معها صاعا من تمر
Its chain of transmission is sahih. As for its first part, it is found in Bukhari 8/175, in the book of seeking permission, chapter "A man should not make another man stand up," and in Muslim 4/1714, number 2177, in the book of greetings, chapter on the prohibition of making a person get up from his place. As for the second part, it has already appeared at 9278, and the third has already appeared at 9889.