Is it permissible to sell a house that was purchased in installments and is still under construction and has not yet been handed over?

It is permissible to sell a house that is still under construction if it has been owned and taken possession of through a lawful قبض (possession). Possession of real estate occurs by way of تخلیة (vacating/clearing), meaning the seller enables the buyer to access it and hands over the key. If possession has been properly established, then its sale is permissible; otherwise, it is not.