It is narrated from Ibn Abbas in Riazun Nazarah that a person asked him, “Was Ali (a.s) himself participating in fighting in the battle of Siffin?” Ibn Abbas said in reply, “I have not seen anyone like him, ever ready to put his life into perils. I used to see him come out fighting bare head (without a helmet), holding the turban in one had and sword in the other. He was so confident of himself that he did not even fear that the enemy may attack his head.”
It is mentioned in Hayatul Haiwan that such powerful was the strike of Ali’s sword that it used to cut everything in half in a single shot. If his sword fell on the head it cut the full body into half and if it fell sideways, it similarly divided the body into half.
Reference :Akhlaq al-A’imma, Morals & Manners of the Holy Imams