All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
If the sale was concluded with its conditions and pillars, then the ownership of the property is transferred to the buyer; in return, the seller gets the price that is agreed upon.
Therefore, the person who bought one-third of the property and paid its price has been owning that part from the time that he purchased it. The fact that the sale was not documented or that the deed of the ownership of the property was not amended is not important.
The seller must deliver the part of the property that belongs to the buyer to him; if he refrains from doing so, then he is unjust and transgresses the right of others. In this case, he is sinful and deserves the threat that applies to a transgressor. The Prophet said, “He who unjustly took a span of land, his neck will be encircled with it down the seven earths.” [Muslim]
It is permissible for this wronged person to take the case to the authorities in order to take his right from the transgressor.
At any rate, it is not permissible for the seller to sell what he does not own from the property without the permission of the owner. If he does so, then his sale is considered an action of a fudhooli (an unauthorized agent), and there is a difference of opinion in regard to its permissibility and validity. The Hanafi and Maaliki Schools, and Ahmad, according to one narration, are of the view that this sale is permissible but its effectiveness depends on the approval of the owner of the sold item. The Shaafi’i School and Ahmad, in the second narration, however, hold the view that this sale is void. Al-Baabarti said in his book Al-‘Inaayah Sharh Al-Hidaayah, “If someone sells the property of someone else without his permission, then the owner has the choice: he can either accept the sale or invalidate it. This is the view of Maalik and Ahmad in one narration. Ash-Shaafi’i said in his new opinion, which is also a narration from Ahmad, 'It (the sale) is not effective because it is not issued by a legitimate owner.'”
According to the view that this type of sale is permissible, the person who owns one-third of the property is entitled to one-third of the total price for which it is sold if the sale is concluded without his permission but he accepted it and approved it.
As for the rent of the property, then the usurping seller is liable to pay the benefits (rent and the like) of a property that is similar to it, throughout the period of his usurpation of the property, if the property is rentable. Ibn Qudaamah said, “The usurper shall guarantee the benefits of the land from the time he usurped it until the time he delivers it (to its owner). This applies to anything that has a price; so the usurper should bear the rent of a land like it, whether he achieved its benefits [i.e. the benefits from the land] or left it until these benefits were wasted, as they were wasted while in his usurping hand, so he should guarantee them, just like wasting items.”
Allaah knows best.