Maliks Muwatta Book 21, Hadith Number 35.

Yahya related to me from Malik from Yahya ibn Said that Umar ibn al-Khattab said, “The nobility of the mumin is his taqwa. His deen is his noble descent. His manliness is his good character. Boldness and cowardice are but instincts which Allah places wherever He wills. The coward shrinks from defending even his father and mother, and the bold one fights for the sake of the combat not for the spoils. Being slain is but one way of meeting death, and the martyr is the one who gives himself, expectant of reward from Allah.”