Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates this statement of the Prophet (peace and blessings be upon him): "The time for Zuhr is when the sun declines and a man's shadow is equal to his height (this remains) until the time for Asr begins. The time for Asr remains until the sun becomes yellow. The time for Isha remains until midnight. (Regarding one word here, the narrator is in doubt.) And the time for Fajr is until the sun rises."