Is it Islamically permissible to consider the installments paid for a piece of land as rent for it, in the event that the buyer is unable to pay for three months, and what are the implications if this condition is void?

It is permissible for the seller to stipulate the right to revoke the sale if the buyer becomes insolvent or fails to receive the price within an agreed-upon period. This falls under the category of the "option of condition" (khiyar al-shart). The seller's revocation due to the buyer's bankruptcy or the inability to collect the price is considered one of the grounds for rescinding the sale. The option remains valid until the end of the period, unless either party benefits from the price or the sold item. If the sale is rescinded due to the inability to pay the full price, the buyer is entitled to reclaim from the seller what they have paid. The seller's condition not to refund a portion of the paid price is void.