Riyad as-Salihin 17:72

Ibn 'Umar (May Allah be pleased with them) said:

A man mentioned to the Messenger of Allah (ﷺ) that he was often deceived in dealings. The Messenger of Allah (ﷺ) said to him, "When you enter into a transaction you should say: "There should be no deception."' [Al-Bukhari and Muslim] .