Sunan Abi Dawud 594
سنن أبي داود#594Da'ifحَدَّثَنَا أَحْمَدُ بْنُ صَالِحٍ، حَدَّثَنَا ابْنُ وَهْبٍ، حَدَّثَنِي مُعَاوِيَةُ بْنُ صَالِحٍ، عَنِ الْعَلاَءِ بْنِ الْحَارِثِ، عَنْ مَكْحُولٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الصَّلاَةُ الْمَكْتُوبَةُ وَاجِبَةٌ خَلْفَ كُلِّ مُسْلِمٍ بَرًّا كَانَ أَوْ فَاجِرًا وَإِنْ عَمِلَ الْكَبَائِرَ " .
Abu Hurairah reported the Messenger of Allah(ﷺ) as saying:The obligatory prayer is essential behind every Muslim, pious or impious, even if he has committed a sins
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 2:204