[21].Al-Anbiya [The Prophets]: Ayat 80

Ayat 80. And We taught him the making of metal coats of mail (for battles), to protect you in your fighting. Are you then grateful?

[Tafseer]  It was We Who taught him the making of coats of mail for your benefit, to guard you from each other´s violence: will ye then be grateful? The making of coats of mails is attributed to David. It is defensive armour, and therefore its discovery and supply is associated with deeds of righteousness in 34:10-11, in contrast with the deadly weapons which man invents for offensive purposes. Indeed, all fighting, unless in defence of righteousness is mere "violence." David's good work then was: (1) he was open to learn wisdom wherever it came from; (2) he sang the praises of Allah, in unison with all nature; (3) he made defensive armour. But all these things he did, because of the faculties which Allah had given him, and we must be grateful for this and for all things to Allah.  

Hazrat Abdullah bin Abu Aufa (May Allah be pleased with them) reported: On one occasion the Messenger of Allah [SAWW](PBUH) was confronting the enemy. He waited until the sun had declined. Then he stood up to address the people and said, "O people! Do not wish for an encounter with the enemy. Pray to Allah to grant you safety; (but) when you encounter them, show patience, and know that Jannah is under the shades of the swords.'' Then he [SAWW](PBUH) said: "Allahumma munzilal-kitab, wa mujriyas-sahab, wa hazimal-Ahzab, ihzimhum wansurna alaihim (O Allah, Revealer of the Book, Disperser of the clouds, Defeater of the Confederates, put our enemy to rout and support us against them).''

[Al-Bukhari Book 04, Chapter 52, Hadith # 210] 

Lesson : as mentioned above in Surah Al-Anbiya Ayat 80."to protect you in your fighting" 

1. From this Hadith we learn that it is better to start war in the afternoon because this was the practice of the Prophet [SAWW](PBUH).

2. The desire for war is prohibited, but when war becomes inevitable, one should not show his back to the enemy; rather, one should fight to the best of his ability and be steadfast in it.

3. Along with steadfastness and patience in fighting, one should also pray for victory because all powers lie with Allah and no one can gain victory without His Will.

The Hadith also mentions a supplication which one should make when he encounters the enemy.