The Spoils of War - 8:41
If you believe in Allah and in that which We sent down to Our servant on the Day of separation, on the Day when the two armies met, then know that one-fifth of every booty that you take belongs to Allah and His Messenger. This share is for the relatives, orphans, the poor and the stranded. Allah is the All-Sufficient.
Why is this share the right of relatives, orphans and the poor?
The Banishment/59:7
What Allah has left as booty for His messenger from the peoples of those countries belongs to Allah and His messenger. So it should be given to relatives, orphans, the poor and the stranded, so that it does not become a monopoly among your rich. Take what the Messenger has given you, but keep away from what he has not given you. Listen to Allah. Allah´s punishment is severe.