The Order of Different Chapters
Question :
How were verses and chapters of the Qur'an ordered? And what was the last verse that was revealed?
Answer:
The Prophet detailed the order of verses and pointed out which verses belonged to which chapter. But as for the order of the chapters, the Prophet arranged some of them and other chapters were ordered through the interpretative judge- ment of others. For example, the Messenger of Allah paired the Surahs Al-Baqarah and Al Imran", because of their super- iority, and the same can be said for these chapters:
Sabih, Al-Ghashiyah, Al-Jumu'ah, and Al-Munafiqun. The point here is that whatever the Prophet arranged, then it is according to his arrangement; and the rest of the chapters were ordered through the interpretative judgement of His Compa- nions, may Allah be pleased with them. With this, then it is not allowed to alter it from what they agreed upon, rather we abide by the order that appears in the Noble Mushaf.
Scholars disagree regarding which verse was revealed last; some say that it is the verse about Riba, while others say that it was:
"This day, I have perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your religion.
Source:
Ibn 'Uthaimin
Fatawa Islamiyah, Vol. 7 Pages 53-54