A while back I was in Morocco, and in the mosque I was praying, the Imam was reciting the Quran in a manner I was not familiar with. I have since learnt that this was called Warsh Nafi. Is it permissible to pray behind such an Imam?
Shia great scholars (Maraaji' of Taqleed) allow reciting Quran in any of the famous seven recitations including the Qira'ah of Warsh, although we believe that the Qira'ah of Hafs from 'Aasim is the most authentic as it was taken from Ameerul Mo'mineen Ali (AS).
We are allowed to pray behind any Muslim following any Muslim sect apart from Shia Islam, but we need to recite Al-Hamd and Sura whispering,bin the first and second Rak'ats for ourselves.
Wassalam.