What is the ruling regarding slandering one's deceased grandfather or father?

Primary text

If a person slanders his grandmother while she is alive, the right of prosecution belongs to her, and her chastity (ihsan) must be considered. If she is deceased, the slanderer may seek the prescribed punishment if he himself is chaste, as the slander constitutes an impugning of his lineage. If the slander is directed at the father, grandfather, or other relatives other than the mothers after their death, the prescribed legal punishment (hadd) is not obligatory according to the apparent view of Khiraqi. This is because the obligation arose concerning the slander of the mother only to establish a right for the speaker due to the negation of his lineage, not a right for the deceased. This view is held by Abu Bakr and the Companions of opinion (Ahl ar-Ra'y).