Musnad Ahmad 652:55

Husayn ibn Ali narrated to us, from Za'idah, from Simak, from al-Nu'man ibn Bashir, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The likeness of the mujahid in the way of Allah is like the likeness of the one who fasts his day and stands [in prayer] his night, until he returns, whenever he returns."