Abu Dawud Book 17, Hadith Number 3494.

Chapter : Not known.

Narated By Anas ibn Malik : During the time of the Apostle of Allah (PBUH) a man used to buy (goods), and he was weak in his intellect. His people came to the Prophet of Allah (PBUH) 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 (PBUH) 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 Apostle of Allah (PBUH) said: If you cannot give up making a bargain , then say: Take , and give, and there is no attempt to deceive.