Afraid of our own sins

Umar Ibn Al-Khattab r.a. said to Saad Ibn Abu Waqqas r.a.:

“I am ordering you and your men to be more afraid of their own sins rather than being afraid of the enemy. Because the sins of the troops are much more dangerous than their enemy is. Muslims win because of the enemy’s sinfulness before Allah. If this were not so, we would not have been able to defeat them, since our number is lesser than theirs and our weapons are not like the ones that they have. If we will be equal with them in sins, they will overpower us. But we are winning with our dignity, but not with our power."