Sahih Muslim Book 20, Hadith Number 4655.

Chapter : Merit of Jihad and of keeping vigilance (over the enemy).

It has been narrated on the authority of Abu Huraira that the Messenger of Allah (may peace be upon him) said: Of the men he lives the best life who holds the reins of his horse (ever ready to march) in the way of Allah, flies on its back whenever he hears a fearful shriek, or a call for help, flies to it seeking death at places where it can be expected. (Next to him) is a man who lives with his sheep at a hill-top or in a valley, says his prayers regularly, gives Zakat and worships his Lord until death comes to him. There is no better person among men except these two.