Al-Matalib al-'Aliyah 255 — The prayer times

Musa bin Mutayr narrates from his father (Mutayr) that he asked Sayyiduna Anas bin Malik (may Allah be pleased with him): "Tell me about the prayer of the Messenger of Allah (peace and blessings be upon him) which he kept to constantly, for it has reached me that he sometimes delayed and sometimes brought forward (the prayer, according to circumstances); but tell me about the manner of the prayer that was his constant practice, as if I were seeing it with my own eyes." He said: "the Messenger of Allah (peace and blessings be upon him) would pray Zuhr when the sun had passed its zenith, and if it was summer he would pray it once it had cooled down (somewhat later). He would pray Asr while the sun was still white and very bright. He would pray Maghrib when the disc of the sun had completely set, and he would finish the prayer while the light of the stars could not yet be seen (clearly in the sky). He would delay the Isha prayer until, when he feared that sleep would overcome the Companions, he would say: 'O Bilal, give the adhan.' And I heard him say: 'Were it not that my Ummah would fall asleep (waiting) for it, I would have loved to delay this prayer to a third of the night or half the night.' And we would leave the Fajr prayer while we could clearly see the light of the stars."
Part of this hadith is also narrated in the books of Sunan through other chains.