Sayyiduna al-Ash'ath bin Qays (may Allah be pleased with him) said: This verse was revealed about me. There was a dispute between me and a man over some property - or land - so I came to the Messenger of Allah (peace and blessings be upon him) and mentioned it to him. He (peace and blessings be upon him) said: "Do you have any witnesses?" I said: No. He (peace and blessings be upon him) said: "Then your opponent will be made to take an oath." I said: Then he will swear. So this verse was revealed: "Indeed, those who sell the covenant of Allah and their oaths for a small price" [Surah Al Imran: 77], to the end of the verse.
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 639