Gandalf on the Ethics of Suicide

[Speaking to Denethor, Steward of Gondor, who was about to burn himself and his son Faramir alive on a funeral pyre]

"Authority is not given to you, Steward of Gondor, to order the hour of your death,' answered Gandalf. 'And only the heathen kings, under the domination of the Dark Power, did thus, slaying themselves in pride and despair, murdering their kin to ease their own death.'"

J. R. R. Tolkien, The Lord of the Rings: The Return of the King