Musnad Abu Ya'la al-Mawsili 160:56

And with his chain of narration, he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The nobility of the believer is his piety, and his chivalry is his intellect, and his lineage is his religion. Cowardice and boldness are instincts that Allah, the Almighty and Majestic, places wherever He wills. The coward flees from his father and his mother, and the bold one fights for that which he does not care if he does not return with it to his family."