He was asked:

A Muslim and a protected non-Muslim jointly own a property which they have demolished completely. May they rebuild it higher than their Muslim neighbour’s property, or not?

He answered:

Praise be to Allah. They may not raise it above the Muslim’s property, for a protected non-Muslim is forbidden to raise his building above a Muslim’s. Whatever must be avoided in order to avoid something forbidden is itself forbidden.

This is analogous to cases in which the unlawful becomes mixed with the lawful, such as when visible impurity becomes mixed with water or other liquids, or when offspring are produced by an animal lawful to eat and one unlawful to eat, such as the simʿ and the ʿisbār (wolf–hyena hybrids), and the mule. The same applies to “cases of indistinguishability,” such as when a man cannot distinguish his sister from an unrelated woman, or a lawfully slaughtered animal from carrion. Since the forbidden cannot be avoided without also avoiding what was originally permissible, both must be avoided. Likewise, whatever action is indispensable to fulfilling an obligation is itself obligatory. This applies only when that action is not a condition for the obligation itself to arise and is within the ability of the person subject to it.

Here, the protected non-Muslim cannot be prevented from raising his building above the Muslim’s unless his partner is also prevented; therefore, both must be prevented. Preventing a Muslim from raising his building above another Muslim’s does not involve raising a non-Muslim’s building above a Muslim’s. This differs from allowing the partner to raise it, for that would entail