[What the guardian of a waqf is permitted to do]

Answer—and Allah is the One who grants success: What is obligatory upon the mutawallī (guardian) is to preserve the mosques’ funds from loss. So if in that there is an interest for the mosque—such as when borrowing them or lending them to another is more conducive to preserving them from loss—then there is no harm in that. This is what the scholars of the madhhab and others have stated.
And I say: It is permissible for the guardian to borrow for himself in case of need and to repay the mosque when it needs [the funds]; for there is no treachery in that and no harm to the mosque, provided he is confident in himself about repayment.
The proof for this is that the Messenger of Allah (May Allah bless him and his family and grant them peace) built his mosque in Madinah on a site that belonged to orphans; their guardian undertook to satisfy them from it, as is mentioned in the books of sīrah.
In this is evidence that the guardian—by virtue of his guardianship—may take something from the orphan’s wealth for himself and consume it, then replace it and make it good; wealth of mosques and the like falls under the same heading. Thus it becomes clear that what is forbidden of consumptions and dispositions is only that which is in the manner of treachery and corruption.
And what supports this is what is reported that ʿAlī (Peace be Upon Him) found a dinar and informed the Messenger of Allah (May Allah bless him and his family and grant them peace)—and ʿAlī (Peace be Upon Him) was in need—so the Prophet (May Allah bless him and his family and grant them peace) permitted him to use it; then the owner of the dinar later came seeking it, and the Prophet (May Allah bless him and his family and grant them peace) gave him a dinar in place of his. The purport of its indication for what we have mentioned is not hidden.
As for lending it to someone else, that is not permissible except on the basis that the guardian himself guarantees [repayment] should the borrower procrastinate or deny [the debt]; otherwise it is not permissible.
This is also indicated by what is narrated regarding the murbad (date-drying yard) which the Messenger of Allah (May Allah bless him and his family and grant them peace) made into a mosque in Madinah.
Yes: What is taken from the murbad story is that it is permissible for the guardian to gift from the orphan’s wealth—on the condition that the orphan is later satisfied about that and that it is replaced with its like or better. The Messenger of Allah (May Allah bless him and his family and grant them peace) accepted the murbad from Abū Ayyūb al-Anṣārī; Abū Ayyūb informed him that it belonged to orphans and that he would satisfy them about it, so the Messenger of Allah (May Allah bless him and his family and grant them peace) accepted the murbad from him, approved his action, and made it a mosque for Allah. This story is well-known in the books of sīrah and histories when speaking about the Prophet’s (May Allah bless him and his family and grant them peace) Migration.
And in the Noble Qur’an is that which supports what this story indicates; Allah Most High says: “And they ask you concerning the orphans. Say: ‘Improvement for them is best. And if you mix with them, then they are your brothers. And Allah knows the corrupter from the reformer. And if Allah had willed, He could have put you into difficulty. Indeed, Allah is All-Mighty, All-Wise.’” [Al-Baqarah:220]. So the verse indicates that there is no blame upon guardians for disposing of part of the orphans’ wealth by way of mixing and the like, and that reform and corruption are the pivot of reward and punishment; thus, if there is nothing of corruption in the disposition, there is no blame—even if there be no [additional] reform therein.
And in al-Bayān: “It is disliked for him (i.e., the guardian of the waqf) to borrow it for himself due to [the appearance of] accusation (tuhmah).” End.
And in the marginal note: “This accusation does not entail prohibition.” End. (Affirmed) (Í) End.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2