Is it permissible to donate a coffin and a washing station for Muslim graves as an ongoing charity on behalf of one's mother?

Perpetual charity is an endowment (waqf), meaning the tying up of the principal and dedicating its usufruct. For example, if you endow something beneficial for the poor, they own its usufruct, while the asset itself remains endowed, not to be sold or given away. Therefore, it is permissible to endow a coffin and a washing station for the deceased and dedicate the reward to the mother.