NAHJUL BALAGHA
SERMON 122
About supporting the weak and the low-spirited during the fighting
Whoever among you feels spiritedness of heart during the action and finds any of his comrades feeling disheartened should ward off (the enemies) from him just as he would do from himself, because of the superiority he enjoys over the other, for if Alláh had willed He would have made the former also like him. Certainly death is a quick seeker. Neither does the steadfast escape it nor can the runner-away defy it. The best death is to be killed. By Alláh in Whose hand (power) lies the life of the son of Abú Tálib, certainly a thousand striking of the sword on me are easier to me than a death in bed which is not in obedience to Alláh.
A part of the same sermon:
It is as if I see you uttering voices like the rustling sound of lizards! You do not seek your own claims nor do you defend against oppression. You have been let free on the path. He who rushes (into the battle) achieves salvation, while he who lags behind, hesitating, gets destruction.