Musnad Ahmad 30:1420

'Affan narrated to us, Hammam narrated to us, Muhammad ibn Jahadah narrated to us, that Abu Husayn narrated to him, that Dhakwan narrated to him, that Abu Hurayrah narrated to him, he said: A man came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, teach me a deed that is equal to Jihad." He said: "I do not find it." He said: "Are you able, when the Mujahid goes out, to enter your mosque, then stand and not grow weary, and fast and not break your fast?" He said: "I am not able." Abu Hurayrah said: "Indeed, the horse of the Mujahid paces in its tether, and for it, good deeds are written for him."