Musnad Abu Ya'la al-Mawsili 115:111

Muhammad ibn Abdullah al-Arzi narrated to us, he said: Abd al-Wahhab ibn Ata narrated to us, he said: Said narrated to us, from Qatadah, from Anas: That a man used to trade during the time of the Messenger of Allah, may Allah bless him and grant him peace, and there was a weakness in his intellect (or his contracts). His family came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, place a restriction (interdiction) upon so-and-so, for he trades and there is a weakness in his intellect." The Prophet, may Allah bless him and grant him peace, summoned him and forbade him from trading. He said: "O Prophet of Allah, I cannot bear to abstain from trading." He, may Allah bless him and grant him peace, said: "If you are not going to abandon trading, then say: 'Take it, for there is no deception (or cheating).'"