the Prophet said: "O Abu Dharr! There will be leaders after me who cause the Salat to die; so perform the Salat during its time. If you pray (with them) during its time, then that will be voluntary Salat for you, if not, then you will have attained your Salat."  

قَالَ النَّبِيُّ ﷺ يَا أَبَا ذَرٍّ أُمَرَاءُ يَكُونُونَ بَعْدِي يُمِيتُونَ الصَّلاَةَ فَصَلِّ الصَّلاَةَ لِوَقْتِهَا فَإِنْ صُلِّيَتْ لِوَقْتِهَا كَانَتْ لَكَ نَافِلَةً وَإِلاَّ كُنْتَ قَدْ أَحْرَزْتَ صَلاَتَكَ وَفِي الْبَابِ عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ وَعُبَادَةَ بْنِ الصَّامِتِ