Amir narrates from Masruq (may Allah have mercy on him) that the Prophet (peace and blessings be upon him) took an oath of abstention (ila') and declared something forbidden to himself, so Allah revealed this verse: "O Prophet, why do you forbid what Allah has made lawful for you?" [Surah al-Tahrim: 1]. He said: "So the forbidden became lawful." And in the verse: "Allah has ordained for you the dissolution of your oaths." [Surah al-Tahrim: 2]
This report is mursal (its chain is broken at the Companion level).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15070