Mishkat al-Masabih 600
Abu Dharr said:
God’s Messenger asked me, “How will you act when you are under rulers who make prayer a dead thing, or delay it beyond its proper time?” When I asked what he commanded me to do he replied, “Observe the prayer at its proper time, and if you can say it along with them do so, for it will be a supererogatory prayer for you.” 

Muslim transmitted it.
وَعَنْ أَبِي ذَرٍّ قَالَ: قَالَ لِي رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: 
" كَيْفَ أَنْتَ إِذَا كَانَتْ عَلَيْكَ أُمَرَاءُ يُمِيتُونَ الصَّلَاةَ أَوْ قَالَ: يُؤَخِّرُونَ الصَّلَاةَ عَنْ وَقْتِهَا؟ قُلْتُ: فَمَا تَأْمُرُنِي؟ قَالَ: " صَلِّ الصَّلَاةَ لِوَقْتِهَا فَإِنْ أَدْرَكْتَهَا مَعَهُمْ فَصَلِّ فَإِنَّهَا لَك نَافِلَة. رَوَاهُ مُسلم