Musnad Ahmad 30:2354

Abu Mu'awiyah narrated to us, he said: Suhayl narrated to us, from his father, from Abu Hurayrah, who said: They said: "O Messenger of Allah, inform us of a deed that equals Jihad in the way of Allah." He said: "You cannot endure it," two or three times. He said: They said: "Inform us, for perhaps we can endure it." He said: "The likeness of the Mujahid in the way of Allah is like the one who fasts and stands (in prayer), the one who is obedient to the verses of Allah, who does not falter from fasting or prayer, until the Mujahid returns to his family."