Musnad Abu Ya'la al-Mawsili 159:144

Abu Hammam al-Walid ibn Shuja' narrated to us, he said: Muhammad ibn Shu'ayb ibn Shabur narrated to me, he said: Shayban ibn 'Abd al-Rahman narrated to me, from 'Abd al-Malik ibn 'Umayr, that he narrated to him, from Muhammad ibn al-Muntashir, from Humayd ibn 'Abd al-Rahman, from Abu Hurayrah, he said: I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: "The best prayer after the obligatory prayer is the night prayer."