It is narrated from Sayyiduna al-Bara' (may Allah be pleased with him) that the last verse to be revealed was: "They ask you for a ruling. Say: Allah gives you a ruling concerning kalalah" [Surah al-Nisa: 176].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12269