What is the ruling on imposing penalty clauses on the lessee in case of delayed payment that increase the amount owed?

Question:
He says: Honorable Shaykh, may Allah grant you success. We have a waqf (endowment), and I am its supervisor. It consists of commercial shops that are rented out, but some of the lessees delay payment for a period that may reach a full year. His question is: Do I have the right to impose penalty clauses on them, such as adding one hundred riyals for every month?

Answer:
No, this is riba (usury or interest); this is the riba. It is not permissible for you to impose the increase. But demand the rent, and if he refuses, complain to the authority so you can take your right from him. The Messenger (peace and blessings be upon him) said: Do not be lenient with him; otherwise, grant him a delay without taking an increase. You may wish to be lenient and tolerant with him, but this is not in the interest of the waqf, and you are a trustee and an agent. This is not in the interest of the waqf. However, if the debt were yours and you were lenient, left it with him, and did not demand it, there is no harm. But if the debt belongs to the waqf, it is not permissible for you to be lenient with it and harm the waqf and those for whom it is established.