It is narrated from Sayyiduna Abdullah bin Amr (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "When you pray Fajr, its time lasts until the first edge of the sun rises; then when you pray Zuhr, its time lasts until Asr arrives; when you pray Asr, its time lasts until the sun turns yellow; when you pray Maghrib, its time lasts until the redness of twilight disappears; and when you pray Isha, its time lasts until the middle of the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1734