That the Prophet (ﷺ) said: "Whoever purchased an animal that has not been milked, then he the choice when he milks it, if he wishes he may return it, returning a Sa' of dried dates along with it."

There are narration on this topic from Anas, and a man from the Companions of the Prophet (ﷺ).
Jami` at-Tirmidhi Book 14, Hadith 51
← Previous Hadith That there was a man who was not very sensible and he would make purchases. So his family came to the Prophet (ﷺ) and said: "O Messenger of Allah! Stop him (from making purchases)." So Allah's Prophet (ﷺ) called him to prohibit him, and he said: "O Messenger of Allah! I have no patience for business." So he said: "When you are buying, say: 'Hand to hand, and no cheating.'"

There is a narration on this topic from Ibn 'Umar.

The Hadith of Anas is a Hasan Sahih Gharib Hadith.

This is acted upon according to the people of knowledge. They say that the free man can be prevented from selling and buying when his intellect is weak. This is the view of Ahmad and Ishaq. Some of the scholars did not think that the free person who had attained the age of responsibility could be prevented from that.

Jami` at-Tirmidhi Book 14, Hadith 50 Next Hadith → That the Prophet (ﷺ) said: "Whoever purchases an animal that has not been milked, then he retains the option for three days. If he returns it, then he is to return with it a Sa' of food, not Samra' "

The meaning of "Not Samra'" is "not wheat."

This Hadith is Hasan Sahih. This Hadith is acted upon according to our companions, among them Ash-Shafi'i, Ahmad, and Ishaq.

Jami` at-Tirmidhi Book 14, Hadith 52