What is the ruling on selling real estate owned by a Muslim to a non-Muslim buyer?

The basic principle is that it is permissible to engage in buying and selling with non-Muslims. The evidence for this is the Prophet's (peace be upon him) purchase of food from a Jew. However, selling becomes unlawful if it leads to harm, such as selling weapons to them to fight Muslims, or selling land and houses to them if their intention is to seize them, or if their purpose is to use them for something forbidden like alcohol.