Abu Hurairah reported,
A man came to the Messenger of Allah ﷺ and said, "Direct me to a deed equal to jihad."He replied, "I cannot find one."Then he said, "When the warrior sets out, can you enter your mosque and stand in prayer without rest, and fast without breaking your fast?"The man said, "Who could do that?"Abu Hurairah said, "Indeed, the warrior's horse prances about on its tether, and good deeds are recorded for him because of it."
Azami 7731
Sahihعن أبي هريرة قال
جاء رجل إلى رسول الله ﷺ فقال: دلني على عمل يعدل الجهاد، قال: لا أجده، قال: هل تستطيع إذا خرج المجاهد أن تدخل مسجدك، فتقوم ولا تفتر، وتصوم ولا تفطر؟ قال: ومن يستطيع ذلك؟ قال أبو هريرة: إن فرس المجاهد ليستن طوله، فيكتب له حسنات.
Bukhari narrated it in the Book of Jihad and Expeditions (2785) through Muhammad bin Hamada, who said, Abu Husayn informed me, that Zakwan told him, that Abu Hurairah 
told him, saying, and then he related it.Muslim narrated it in the Book of Leadership (1878:110) through Suhayl bin Abu Salih, from his father, from Abu Hurairah, who said, and then he related it similarly, and in it, "The example of one who strives in the cause of Allah is that he does not tire from fasting or prayer until the mujahid returns from striving in the cause of Allah, Most High." It does not contain Abu Hurairah's statement, "Indeed the mujahid's horse..."His saying "yastannu" means it frolics energetically. His saying "tawaluhu" refers to the rope with which the animal is tethered, one end of it is held while the other is let out into the pasture.