The obligatory prayer is essential behind every Muslim, pious or impious, even if he has committed a sins.  

قَالَ رَسُولُ اللَّهِ ﷺ الصَّلاَةُ الْمَكْتُوبَةُ وَاجِبَةٌ خَلْفَ كُلِّ مُسْلِمٍ بَرًّا كَانَ أَوْ فَاجِرًا وَإِنْ عَمِلَ الْكَبَائِرَ