Musnad Ahmad 30:3784

Hisham ibn Abd al-Malik al-Tayalisi narrated to us, Abu 'Awanah narrated to us, from 'Abd al-Malik, from Humayd ibn 'Abd al-Rahman, from Abu Hurayrah, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The best prayer after the obligatory prayer is the night prayer, and the best fasting after Ramadan is the month of Allah, which you call al-Muharram."