“In the time of sleep this body is as though dead; it does not see nor hear; it does not feel; it has no consciousness, no perception—that is to say, the powers of man have become inactive, but the spirit lives and subsists. Nay, its penetration is increased, its flight is higher, and its intelligence is greater. To consider that after the death of the body the spirit perishes is like imagining that a bird in a cage will be destroyed if the cage is broken, though the bird has nothing to fear from the destruction of the cage. Our body is like the cage, and the spirit is like the bird. We see that without the cage this bird flies in the world of sleep; therefore, if the cage becomes broken, the bird will continue and exist. Its feelings will be even more powerful, its perceptions greater, and its happiness increased.”
-‘Abdu’l-Baha, Some Answered Questions, p. 228