Is it permissible, Islamically, to gift an undivided share (such as one-sixth) of an inherited property that cannot be divided, to a person who is not among the heirs?

It is permissible for a person to donate their undivided share in a property according to the majority of scholars. Pre-emption (shafa'a) does not apply to a donation (hiba) because it is not a contract of exchange. There is no difference in the donation between an heir and a non-heir if it occurs during the donor's sound health. However, if it occurs during a life-threatening illness, it takes the ruling of a will.