The Ninth Sphere also refers to the lowest sphere of the inferior worlds (Hell, Klipoth).
"The great Master Hilarion IX said that in ancient times, to descend into the Ninth Sphere was the maximum ordeal for the supreme dignity of the Hierophant. Hermes, Buddha, Jesus Christ, Dante, Zoroaster, Mohammed, Rama, Krishna, Pythagoras, Plato and many others, had to descend into the Ninth Sphere in order to work with the fire and the water which is the origin of worlds, beasts, human beings and Gods. Every authentic white Initiation begins here." —Samael Aun Weor, The Aquarian Message