A man displayed his merchandise in the market and swore that he had been offered for it more than he had actually been offered, in order to deceive a Muslim into buying it. Then this verse was revealed, "Indeed, those who exchange the covenant of Allah and their oaths for a small price" [Al Imran 3:77], to the end of the verse.
أن رجلا أقام سلعة في السوق، فحلف فيها: لقد أعطى بها ما لم يعطه، ليوقع فيها رجلا من المسلمين، فنزلت: {إن الذين يشترون بعهد الله وأيمنهم ثمنا قليلا} إلى آخر الآية.