Question Summary:
Sajadah sahw behind the Imam

Question Detail:

I was reading Namaaz with jamaat and I made a mistake under which sajdah sahw becomes mandatory, but I did not make sajdah sahw, will my namaaz be valid or not? 

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
If a person is performing Salah with jama’ah behind the Imam and he commits a mistake which normally necessitates sajdah sahw, he should not make the sajdah sahw. Sajdah of sahw is obligatory only on a person leading the prayer (Imam) or on a person praying individually (Munfarid). Therefore, your Salah will be valid without the sajdah sahw.[1]
 
And Allah Ta’āla Knows Best
Asim Patel
Student Darul Iftaa
Venda, South Africa
Checked and Approved by,
Mufti Ebrahim Desai.
www.daruliftaa.net