Sri Aurobindo translates Prashna Upanishad, Fourth Question, Verses 7-11: “”O fair son, as birds wing towards their resting tree, so do all these depart into the Supreme Spirit: Earth and the inner things of earth: water and the inner things of water: light and the inner things of light: air and the inner things of air: ether and the inner things of ether: the eye and its seeings: the ear and its hearings: smell and the objects of smell: taste and the objects of taste: the skin and the objects of touch: speech and the things to be spoken: the two hands and their takings: the organ of pleasure and its enjoyings: the anus and its excretions: the feet and their goings: the mind and its feelings: the intelligence and what it understandeth: the sense of Ego and that which is felt to be Ego: the conscious heart and that of which it is conscious: light and what it lightens: Life and the things it maintaineth. For this that seeth and toucheth, heareth, smelleth, tasteth, feeleth, understandeth, acteth, is the reasoning self, the Male within. This too departeth into the Higher Self which is Imperishable. He that knoweth the shadowless, colourless, bodiless, luminous and imperishable Spirit, attaineth to the Imperishable, even to the Most High. O fair son, he knoweth the All and becometh the All. Whereof this is the Scripture: He, O fair son, that knoweth the Imperishable into whom the understanding self departeth, and all the Gods, and the life-breaths and the elements, he knoweth the Universe!’ ”
The Rishi describes the state of deep sleep as one in which all of the senses, objects of senses and powers of awareness are withdrawn from the outer world and focused on the Supreme. The “Male” within is a translation of the term Purusha, elsewhere described by Sri Aurobindo as the witness consciousness or as the Knower within, with an understanding that the “Female” is the power of Nature in action. The status of deep sleep is then transitioned into a discussion of the status of attaining knowledge of the Eternal. This knowledge is a knowledge by identity, which means “he knoweth the All and becometh the All.” This status implies that he knows the Eternal, Immutable Self beyond the manifestation, as well as the entire manifested universe. The state of deep sleep is thus used as a means of describing the withdrawal of the conscious awareness from the Many in order to merge with the One, and as a metaphor for the merging of the consciousness into the One in the fourth state of consciousness, called turiya.
Sri Aurobindo, The Upanishads, Prashna Upanishad, pp.297-315