Musnad Ahmad 32:371

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Abu Sadaqah, the freed slave of Anas, who said: I asked Anas about the prayer of the Messenger of Allah, peace and blessings of Allah be upon him, and he said: "He used to pray Dhuhr when the sun passed the meridian, and ‘Asr between these two prayers of yours, and Maghrib when the sun set, and ‘Isha when the twilight disappeared, and Subh when the dawn broke, until the eyesight became clear."