Sahih al-Bukhari 4364
Narrated Al-Bara:
The last Sura which was revealed in full was Baraa (i.e. Sura-at-Tauba), and the last Sura (i.e. part of a 
Sura) which was revealed was the last Verses of Sura-an-Nisa':-- "They ask you for a legal decision. 
Say: Allah directs (thus) About those who have No descendants or ascendants As heirs." (4.177)
حَدَّثَنِي عَبْدُ اللَّهِ بْنُ رَجَاءٍ، حَدَّثَنَا إِسْرَائِيلُ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْبَرَاءِ ـ رضى الله عنه ـ قَالَ آخِرُ سُورَةٍ نَزَلَتْ كَامِلَةً بَرَاءَةٌ، وَآخِرُ سُورَةٍ نَزَلَتْ خَاتِمَةُ سُورَةِ النِّسَاءِ ‏{‏يَسْتَفْتُونَكَ قُلِ اللَّهُ يُفْتِيكُمْ فِي الْكَلاَلَةِ‏}‏