I would like to know your opinion on a man who leases his shop to a man in return for a specified monthly or annual rent. The condition between them was that the owner had no right to ask the lessee to leave the shop or to rent it to another person unless the owner has to reconstruct the shop. Is this contract flawed because of not specifying the period of rent or for any other reason? If it is flawed, what is the approved way out under Sharee'ah to be followed? What should the person who made this mistake do?
May Allaah reward you.

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The validity of a rent contract is conditioned with specifying the period at which the rental ends. If this period is not clarified, then, the rent contract is defective and nullified.

Ibn Qudaamah said, “Ibn Al-Munthir said, ‘All scholars – from whom we learned – unanimously agree that it is permissible to rent houses and animals and their rental is permissible only in case of stating a specified known period.’”

This stipulated condition by the lessee will make the period of rental unknown; accordingly, the rent contract would be defective for not specifying the period of time. Such a contract must be rescinded, then, the lessor has the right either to rent the shop to the lessee in question or to anyone else in accordance to Sharee'ah rules of rental.

We bring to attention that it is impermissible for the lessee to hold on to the rent contract whose duration was unspecified, even if his situation is strengthened by a defective contract or man-made laws that allow for that. The lessee should be aware that every condition or law that contradicts the ruling of Allaah is void and one should submit to the ruling of Allaah and His Messenger, sallallaahu ‘alayhi wa sallam. Allaah Almighty says (what means): {The only statement of the [true] believers when they are called to Allaah and His Messenger to judge between them is that they say, "We hear and we obey." And those are the successful.} [Quran 24:51]

Allaah Knows best.