peace
In the quran, it says "labus lakum litahsinukum min busikum"
this is coming from a native arabic speaker
Labus is plural of libs, which means clothing
thee translation for this would be "clothes for you to defend against the enemy"
clothes tod fend yourselves with is not neccasarily mail, it could be any armour. wikipedia says european mail is dated in the 3rd century bc, david was not european nor does the verse say specifically mail
i hope i helped, peace.