A man mentioned to the Messenger of Allah ﷺ that he was being deceived in business transactions. The Messenger of Allah ﷺ said to him, "When you make a sale, say, 'No deception.'" So whenever the man made a sale, he would say, "No deception."
أخبرنا قتيبة بن سعيد عن مالك عن عبد الله بن دينار
أن رجلا ذكر لرسول الله ﷺ أنه يخدع في البيع فقال له رسول الله ﷺ إذا بعت فقل لا خلابة فكان الرجل إذا باع يقول لا خلابة
Sourced from Bukhari, Sales, Chapter on What Is Disliked of Deception in Sales, Hadith No. 2117, from the hadith of Malik, and Muslim, Sales, Chapter on One Who Is Deceived in a Sale, Hadith No. 1533, from the hadith of Abdullah bin Dinar, with this wording. It is also found in Muwatta (Yahya): 22/685, and in Kubra, Hadith No. 6076.