What is the ruling of Islamic law regarding a father who doubts the lineage of his son, and how should he deal with this doubt, knowing that he has divorced the wife and the son is still with him?

The father must fear Allah and repent to Him for slandering his wife and disowning his son based on doubt, as doubt is not permissible as a basis for slander or for denying parentage. Rather, there must be certain conviction or strong presumption. The retention of the child and the failure to declare his disownment are evidence of acceptance of his lineage, so it is not permissible to disown him thereafter. One must be wary of disowning a child unjustly, for a severe warning has been issued regarding this, that whoever disavows his child while looking at him, Allah will veil Himself from him and expose him before the first and the last generations.