That the Prophet (ﷺ) said: "Do not go out to meet the market (caravan), do not leave animals un-milked (to deceive the buyer), nor out-spend one another."

There are narrations on this topic from Ibn Mas'ud and Abu Hurairah. The Hadith if Ibn 'Abbas is a Hasan Sahih Hadith. This is acted upon according to the people of knowledge, they dislike selling the Muhaffalah, and it is the Musarrah that has not been milked by its owner in days or more than that, so the milk accumulates in its udder to impress the purchaser. This is a type of deceit and misrepresentation.

Jami` at-Tirmidhi Book 14, Hadith 70