Abu Hurairah narrated that :Allah’s Messenger said: “Indeed for (the time of) Salat (there is a) beginning and an end. The beginning of the time for the Zuhr prayer is when the sun passes the zenith, and the end of its time is when the time for Asr enters. The beginning of the time for the Asr [prayer] is when its time enters, and the end of its time is when the sun yellows (turns pale). The beginning of the time of Maghrib is when the sun as set, and the end of its time is when the twilight has vanished (i.e., the horizon is invisible because of darkness). The beginning of the time for Isha, the later one, is when the horizon has vanished, and the end of its time is when the night is at its half. The beginning of the time for Fajr is when Fajr begins, and its end is when the sun rises.”
Abu Dharr narrated that :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.”
Ibn Abbas narrated:”The Prophet only performed the two rak’ah (units of prayer) after Asr because some wealth came to him which distracted him from the two rak’ah after Zuhr, so he prayed them after Asr, then he did not repeat that.”