Musnad Ahmad 658:166

Hujayn narrated to us, Isra'il narrated to us, from Abu Ishaq, from Al-Bara' who said: "The last Surah that was revealed to the Prophet, may Allah bless him and grant him peace, in its entirety was Bara'ah (At-Tawbah). And the last verse that was revealed was the conclusion of Surah An-Nisa': 'They ask you for a legal ruling' [An-Nisa': 176] until the end of the Surah."