Abu 'Imran al-Jauni عبد الملك بن حبيب أبو عمران الجوني · The Book on Salat (Prayer)

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."