Musnad Ahmad 32:448

Bahz narrated to us, Hammad—meaning Ibn Salamah—narrated to us, he said: Musa Abu al-Ala narrated to us, from Anas ibn Malik, "That the Messenger of Allah (peace and blessings of Allah be upon him) used to pray during the days of winter, and we did not know whether more of the day had passed or more of it remained."