Sahih Muslim Book - 33, Hadith - 4800

حَدَّثَنَا هَدَّابُ بْنُ خَالِدٍ الأَزْدِىُّ حَدَّثَنَا هَمَّامُ بْنُ يَحْيَى حَدَّثَنَا قَتَادَةُ عَنِ الْحَسَنِ عَنْ ضَبَّةَ بْنِ مِحْصَنٍ عَنْ أُمِّ سَلَمَةَ أَنَّ رَسُولَ اللَّهِ -صلى الله عليه وسلم- قَالَ « سَتَكُونُ أُمَرَاءُ فَتَعْرِفُونَ وَتُنْكِرُونَ فَمَنْ عَرَفَ بَرِئَ وَمَنْ أَنْكَرَ سَلِمَ وَلَكِنْ مَنْ رَضِىَ وَتَابَعَ ». قَالُوا أَفَلاَ نُقَاتِلُهُمْ قَالَ « لاَ مَا صَلَّوْا ».

It was narrated from Umm Salamah that the Messenger of Allah (s.a.w) said: "There will be rulers (whose good deeds) you approve of and (whose bad deeds) you object to. Whoever recognizes (their bad deeds as such) will be free of blame, and whoever objects to (their bad deeds) will also be safe, but whoever approves and follows (is blameworthy)." They said: "Should we not fight them?" He said: "No, not so long as they offer prayers."