Abu Dawood: Hadith 3502

During the time of the Messenger of Allah (ﷺ) a man used to buy (goods), and he was weak in his intellect. His people came to the Prophet of Allah (ﷺ) and said: Prophet of Allah, stop so-and-so (to make a bargain) for he buys (goods), but he is weak in his intellect. So the Prophet (ﷺ) called on him and forbade him to make a bargain. He said: Prophet of Allah, I cannot keep away myself from business transactions. Thereupon the Messenger of Allah (ﷺ) said: If you cannot give up making a bargain , then say: Take , and give, and there is no attempt to deceive.