First:

When the founder of an endowment specifies a fixed number of dirhams from an endowment yielding a certain revenue, he may intend a proportion: for example, he may stipulate ten for someone when the revenue is one hundred, intending one tenth. If contextual evidence indicates that this was his intention, it should be acted upon. It is customary that, if an endowment yields one hundred dirhams and the founder stipulates six for someone, then its revenue rises to five hundred, the amount stipulated in such circumstances would increase proportionately—for example, fivefold. It is not customary for someone who stipulates six out of one hundred to stipulate only six out of five hundred. People’s words should therefore be understood according to their customary manner of expression.

Second:

Even if the founder had not stipulated this, the endowment’s surplus should be spent on purposes comparable or similar to its own, such as other mosques, poor neighbours, and the like. The alternatives are either to spend it on such purposes or to hold it in reserve for future repairs and similar needs.

Keeping it in reserve indefinitely while the revenue continues to increase serves no purpose. Rather, it is harmful, since it holds the money for unjust officials and administrators who assume authority over them and take it without right.

It is reported that ‘Alī ibn Abī Tālib urged people to raise money for a slave who had contracted to purchase his freedom. When some money remained, he ordered that it be spent on other slaves with such contracts. The reason is that, when funds cannot be spent on their specifically designated purpose, they are directed to another of the same kind. This is therefore the sound view concerning endowments, and any surplus from their coverings should be given in charity, just as ‘Umar ibn al-Khattāb used to give the covering of the Kaaba in charity each year, distributing it among the pilgrims.