Question Summary:
Is it allowed to pray salah behind the Imam who is Barelwi?

Question Detail:

Is it allowed to pray salah behind the Imam who is Barelwi?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
 
It is impermissible to perform Salah behind an Imam who possess beliefs of Shirk (associating partners with Allah). However, if his beliefs do not tantamount to shirk his beliefs do not negate Imaan, then performing Salaah behind this Imam will be correct. If you are unaware of his beliefs, then you should go to an alternative masjid.[i]
 
And Allah Ta’āla Knows Best
 
Saanwal ibn Muhammad,
Student Darul Iftaa
UK   
 
Checked and Approved by,
Mufti Ebrahim Desai Saheb