Sahih Bukhari, Chapter: Jihaad (Fighting for the cause of Allah)

The Prophet (SAW) said, " Let the slave of Dinar and Dirham, of Qatifa and Khamisa perish as he is pleased if these things are given to him, and if not, he is displeased. Let such a person perish and relapse, and if he is pierced with a thorn, let him not find anyone to take it out for him. Tuba (all kinds of happiness or a tree in Paradise) is for him who holds the reins of his horse to strive in Allah's Cause, with his hair unkempt and feet covered with dust: if he is appointed in the vanguard, he is perfectly satisfied with his post of guarding, and if he is appointed in the rear guard, he accepts his post with satisfaction; (he is so simple and unambituous that) if he asks for permission he is not permitted, and if he intercedes, his intercession is not accepted."