Is it permissible for parents to disown their children or vice versa, or for a brother to disown his brother, and when is such disownment legitimate, and what rulings result from it?

The aforementioned disavowal depends on what is intended by it:

1. If what is intended is disavowal of evil deeds: This is permissible, as in the Almighty's saying: "But if they disobey you, say, 'Indeed, I am disassociated from what you do'," where it shows disapproval of disobedience.

2. If what is intended is the denial of lineage: This is not permissible except in specific cases. The reasons for establishing lineage are four: the marital bed (al-firash), acknowledgment (al-istilhaq), clear evidence (al-bayyinah), and divination by tracing footsteps (al-qafah). For someone whose lineage is established by one of these reasons, it is not permissible to deny it, due to the severe warnings mentioned concerning this, such as the hadith: "Any man who disowns his child while looking at him, Allah will veil Himself from him and expose him before the heads of the first and the last." An exception to this is the denial of a child through li'an (oath of condemnation) if the husband knows of his wife's adultery. As for attributing oneself to other than one's father, it is forbidden, due to the Prophet's (peace be upon him) saying: "Do not desire to be other than your fathers, for whoever desires to be other than his father is an act of disbelief."

Accordingly, it is forbidden for a father to deny his children without a legal justification, or for children to deny their affiliation with their father, as well as for a brother or sister to deny the lineage of their brother or sister. The legal implications of lineage, such as inheritance and agnation, cannot be lifted by anyone.