We have shared earlier from Bukhari that all the Companions run away from the battle of UHUD only 12 people remained with the Holy Prophet.
We also shared from the battle of Hunain that all the Companions run away from the battle of Hunain including Umar bin Khattab only few people remained with the Holy Prophet(pbuh).
We want to share from the Holy Quran that it is so much severe to run away in battles with pagans, (8-15-16)
" O you who have believed, when you meet those who disbelieve advancing [for battle], do not turn to them your backs [in flight]. And whoever turns his back to them on such a day, unless swerving [as a strategy] for war or joining [another] company, has certainly returned with anger [upon him] from Allah, and his refuge is Hell - and wretched is the destination".
We also want to share from the Holy Quran, this is one of the criteria by Allah(swt) to be strong and brave enough to lead the people after the Prophet.
“And their Prophet said to them: Surely Allah has raised Talut to be a king over you. They said: How can he hold kingship over us while we have a greater right to kingship than he, and he has not been granted an abundance of wealth? He said: Surely Allah has chosen him in preference to you, and He has increased him abundantly in knowledge and physique, and Allah grants His kingdom to whom He pleases, and Allah is All-Sufficient for His creatures' needs, All-Knower."
-Surah Baqarah (2:247)
In above verse of the Holy Quran, we know that Allah appointed the deputy of Prophet and a chief for the people. We also found the criteria that who can be the best leader.
That person must have these two qualities, best knowledge and physique (strong nerves).
Please read the narration in Nissaie about khayber.
English Translation
Abu Laila Narrated:
He asked Imam Ali while he was going with them that people get surprise at you because you wear light (thin) dress in winter and in hot summer you wear heavy clothes. Imam Ali asked Abu Laila, were you not with us in the battle of Khaiber, Abu laila replied, surely I was there with you. Imam Ali said:
The Holy Prophet gave flag of Army and sent him to fight, he came back (without victory), then the Prophet gave flag to Umar bin Khattab, he also came back with his men. The Holy Prophet said: Surely I will give flag to the man who loves Allah and his Prophet also Allah and his Prophet love him. He keeps on attacking repeatedly, he never runs away. The Holy Prophet sent his message to me while I had eye sore. The Holy Prophet put his saliva on my eyes and prayed about me “O Allah save him from the difficulties of winter and cold”.
Imam Ali said:
“after this prayer of the Holy Prophet about me, I never had any problem with cold and hot weather.”
Arabic Narration with Urdu Translation
Please another narration with different chain
English Translation
Abdullah bin Buraidad reported:
I heard from Abu Buraidah that we surrounded Khaiber, Abu Baker carried the flag of Muslim army but he could not gain victory. Next day Umar bin Khattab got the flag, he also returned back and could not get victory that was the difficult day for Muslims. Then the Holy Prophet said:
I will give the flag tomorrow to the person who loves Allah and his Prophet also Allah and his Prophet love him. He won’t return back until Allah will give victory.
(We have translated the important part, rest of the story is almost the same. The flag was given to Imam Ali(as) and Imam Ali got the victory. Buraidah said “I was among those who wished to get flag next morning”)
Please read the next part
Please read the next part with Urdu translation 
Please read another naration with the different chain.
English translation
Buraidah Aslami narrated:
When The Holy Prophet reached Khaiber, at the day of Khaiber, The Holy Prophet gave the flag to Umar bin Khattab, some people from Muslims joined him. Umar bin Khattab got defeated with his man, they came back to the Holy Prophet. The Holy Prophet said:
“Surely I will give flag to the man who loves Allah and his Prophet also Allah and his Prophet love him.”
(We have translated the important part of the narration, Abu Bakar and Umar were among those who wished to get the flag next day, rest of the narration says, the flag was given to Imam Ali, Imam Ali got the victory).
Please read with Urdu translation
