Narrated `Abdullah bin Abu `Aufa:
A man displayed some merchandise in the market and took an oath that he had been offered a certain price for it while in fact he had not, in order to cheat a man from the Muslims. So then was revealed:-- "Verily! Those who purchase a small gain at the cost of Allah's Covenant and their oaths..."(3.77)
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 73
Arabic reference: Book 65, Hadith 4551