Question Summary:
Is the sequence of the Surahs necessary in Salah?

Question Detail:

 
We know that we have to do recitation of surahs during salah in the same sequence as in the Quran. Do we have to offer Sajda e Sahw if we have mistakenly broken this sequence during namaz.
Example: In the first Raka of fajr I recited Surah Falaq. In the second Raka I recited Surah Kosar. 

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The Surahs of the Qur’an should be read in the sequence of the Qur’an. As such, after reading Surah Al-Falaq, you should read Surah An-Nās (as you already know).
Nevertheless, Sajdah-e-Sahw will not be compulsory upon you if you broke the sequence by reciting a Surah prior to the one already recited.[1]
 
And Allah Ta’āla Knows Best
AbdulMannan Nizami
Student Darul Iftaa
Chicago, IL, USA 
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net