[Ruling on a son whose father consumes the waqf’s yields]

Answer—and Allah is the One who grants success and aid: The son does not have to guarantee what has been eaten:
1. Because the father is the liable party due to consumption; milling and baking are juridical consumption. They have said that by consumption the item becomes the property of the consumer; at that point the liability transfers to the consumer’s obligation: fungible goods are guaranteed with their like, and non-fungibles with their value.
On this basis, it is permissible for the son to eat with his father. They have adduced as support the report that a man slaughtered a sheep as an honor for the Prophet (May Allah bless him and his family and grant them peace); then it became clear to the Prophet (May Allah bless him and his family and grant them peace) that the sheep was stolen, so he did not eat from it and ordered that it be given as food to some of the needy—this is the purport of the narration.
2. The son may deem that he is eating from his father’s share which the father takes in return for his labor.
3. And since the questioner is a poor seeker of knowledge, he falls among the disbursement categories of that waqf; for the said waqf is, as appears to me, dedicated to the weak and the needy. And Allah knows best.
Accordingly, let the son eat with the intention that this is a disbursement upon himself, and he need not avoid eating in his father’s house.
As for helping his father with ploughing and cultivating the waqf, there is no harm upon him in that and no sin—if Allah wills—since this is not assistance in sin and transgression; sin and transgression lie in withholding the poor’s and needy’s share, preventing them from it, and consuming it; cultivation and tillage are not of that.
If it be said: The guardianship has lapsed here due to betrayal, so cultivation and tillage would be transgression, and assistance would then be impermissible—
We say: Dismissing such a person requires a judge appointed by the Muslim ruler, or a muḥtasib, or a competent authority, or an appointee of the Five. If none of that exists, guardianship remains presumed. And if this guardian does not step down and remove himself from the waqf, his guardianship remains as we have said.
The proof for what we have said is what is reported from the Commander of the Faithful ʿAlī (Peace be Upon Him) in Nahj al-Balāghah: he used to threaten some of his governors who showed signs of treachery and warn them with removal and stern punishment. It is not reported that he renewed the appointment for those from whom treachery had appeared; rather he would call them to abandon treachery and repent from what they had committed. If treachery itself constituted dismissal, a new appointment would have been necessary; since nothing of that appears, we know that treachery is not, by itself, a dismissal.
And this, it appears, is the practice with the Muslim authorities in former and latter times.

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