Musnad Ahmad 32:691

Abu Kamil and 'Affan narrated to us, they said: Hammad ibn Salamah narrated to us, from Musa Abu al-'Ala'. And 'Affan said in his narration: Musa Abu al-'Ala' narrated to us, from Anas ibn Malik, who said: "The Prophet, peace and blessings of Allah be upon him, used to pray the Dhuhr prayer during the days of winter, and we did not know whether more of the day had passed or what remained of it."