Is it permissible to cancel a contract for the sale of a house for which the full price has not been paid by the buyers, and is the contract considered canceled according to the verbal agreement between the seller and the buyer?

If the house is jointly owned by siblings and undivided, then the brother has the right of pre-emption in purchasing it, as long as he does not demand to buy it for less than the price or postpone payment when a cash buyer is available. The Prophet, peace be upon him, decreed pre-emption in every partnership that has not been divided. However, after division, pre-emption is not obligatory according to the majority of scholars.

As for selling with the condition of "cash option," meaning that if the buyer does not pay the price within a known period, then there is no sale between them, scholars have differed regarding its permissibility:

- Hanafi and Hanbali schools: They consider it permissible due to the strength of its evidence, its reported practice by Umar, may Allah be pleased with him, and because the default rule for conditions is permissibility. - Shafi'i school: They consider the contract invalid because it entails suspending the annulment of the sale based on uncertainty (gharar). - Maliki school: They have multiple opinions on this issue.

The preponderant opinion is that of the Hanafi and Hanbali schools, which permits the condition and validates the sale. Consequently, the contract is rescinded if payment is not made within the specified period. Therefore, these contracts must be terminated to absolve the deceased brother's debt.