Subala Upanishad of Shukla-yajurveda, Chapter IV

"In the middle of the heart is a red fleshy mass in which is the dahara-lotus. Like the lotus, it opens into many (petals). There are ten openings in the heart. The (different kinds of) prāṇas are located there. Whenever he (Ātmā) is united with prāṇa, he sees cities with rivers and other variegated things; when united with vyāna, he sees Devas and Ṛṣis; when united with apāna, he sees Yakṣas, Rākṣasas and Gandharvas; when united with udāna, he perceives the celestial world, Devas, Skanda (Kārtikeya or the six-faced Mars), and Jayanta (Indra's son); when united with samāna, he sees the celestial world and the treasures (of Kubera); when united with rambhā (a nādi hereafter given out), he sees whatever is seen or not seen, heard or not heard, eaten or not eaten, asat or Sat and all else.

"There are ten midis; in each of these are seventy-one. And these become 72,000 branch nādis. When Ātmā sleeps therein, it produces sound; but when Ātmā sleeps in the second kośa (or sheath) then it sees this world and the higher as also knows all the sounds. This is spoken of as samprasāda (deep sleep rest). Then prāṇa protects the body. The nādis are full of blood, of the colours green, blue, yellow, red, and white. Now this dahara-lotus has many petals like a lily. Like a hair divided into 1,000 parts, the nādis called hita are. The divine Ātmā sleeps in the ākāś of the heart, in the supreme kośa (or ānandamaya sheath); sleeping there, it has no desires, no dreams, no deva-worlds, no yajñas or sacrificer, no mother or father, no relative, no kinsman, no thief, or no Brahman-slayer. Its body is tejas (resplendent effulgence) and of the nature of nectar (or the immortal). It is as if in sport, a water-lotus. When he returns again to the waking state by the same way (he quitted or went in before to the heart), he is Samrāt^[1]. Thus says he."