Does the condition that the participant is not entitled to any of their payments (Takaful or investment) upon withdrawal before eighteen months affect the Islamic permissibility of Takaful insurance?

The inclusion of a clause in a Takaful (Islamic cooperative insurance) contract stipulating that a withdrawing participant voluntarily donates their paid installments and their share of the surplus from the investment of the donation funds, is permissible. It does not negate its nature as a cooperative and Takaful arrangement.