When the day came that the famous combat of Kheybar took place, and after the great heroism of Ali Ibn Abi Tâléb before the great gates of Kheybar’s fortress, the war ended finally, and victory belonged to Muslims.
There was a little village near Kheybar by the name of “Fadak’’; its Jewish inhabitants had made peace with the Prophet. They had offered him half of their village to make peace with him, and to show him their loyalty;
In return, they had asked the permission to remain in their homeland. This piece of land became a possession of the Prophet. The Messenger of God gave the money that came from his land to the poor families of Bani Hashem Tribe.
But with the coming of the sourate : Ar- Roum, [where it said]: ‘‘You should give your relatives’ due’’, the Messenger of God, offered Fadak to Fâtemeh, by God’s Command.
source : http://www.maaref-foundation.com