Nahjul Balagha Part 2, Letters and Sayings

Letter 16: His advice to his followers during a battle

He used to give to his followers at the time of battle

The retreat after which return is intended and the withdrawal after which attack is in view should not make you unhappy. Do justice with the swords (allow your swords to do their duties). Keep ready a place for the falling of bodies (of your foe); prepare yourselves for hurling strong spears and striking swords with full force, and keep your voices down as that keeps off cowardice.

By Him Who broke open the seed (for growing) and created living beings, they had not accepted Islam but they had secured safety (by verbally professing it) and had hidden their misbelief. Consequently when they found helpers for their misbelief they disclosed it.