Sahih Muslim | Book 10 | Chapter 12
Narrated by Abdullah b. Dinar
Abdullah b. Dinar narrated that he heard Ibn 'Umar (Allah be pleased with them) saying: A man mentioned to the Messenger of Allah (may peace be upon him) that he was deceived in a business transaction, whereupon Allah's Messenger (may peace be upon him) said: When you enter into a transaction, say: There should be no attempt to deceive.