Amr bin Shu'ayb (may Allah have mercy on him) narrates from his grandfather (may Allah be pleased with him) that a man asked the Messenger of Allah (peace and blessings be upon him) about the prayers. He (peace and blessings be upon him) led Zuhr when the shadow had begun to return, led Asr when the shadow of everything had become equal to it, led Maghrib when the sun had set, led Isha when the redness of twilight had disappeared, and led Subh when the first light of dawn appeared. Then on the second day he led Zuhr when the shadow of everything had become equal to it, led Asr when the shadow of everything had become twice its length, led Maghrib when the sun had set, led Isha in a third of the night, and led Subh after it had become light. Then he said: "Jibril (peace be upon him) led me in prayer so that he may teach you that between these two times is the time of prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1721