Muslims can take booties left by enemies who ran away in fear of Muslim army. They are called “Fay”; they could be given to the poor or the ruler decides how they will be used in the best interest of the community.
Gains without battle
Fay’ is an Arabic term that refers to what Muslims gain from their enemy in a legitimate way, without fighting, such as booty left behind by unbelievers who fled when they heard of the approach of the Muslim army. This type of gain is spent as the Muslim ruler determines to be in the best interests of the Muslim community.
:Umar reported
‘The property left by the al-Nadir tribe was fay’ granted by Allah to His messenger, as the Muslims did not use their horses or arms during the confrontation. As such, they belonged totally to Allah’s messenger. He used it to give to his family and the poor in the Muslim community, and used any residue to buy arms and equipment for future jihad campaigns’
Related by al-Bukhari, hadith No. 2,904; Muslim, hadith No. 1,757.