12 Steps to Attain Immortality

218. Devi said: Deva, Deva, Mahadeva, O God of all gods, in this universe who is the greatest friend of humans and what is that by which all desires can be fulfilled?

219. Ishwara said: Prana is the greatest friend, prana is the greatest companion. O fair-faced one there is no closer friend in this universe than prana.
220. Devi said: How does the air reside in the prana, and is the body in the form of prana? How is the prana moving in the tattwas perceived by the yogis?
221. Shiva said: Residing in the centre of this body, prana vayu is like a guard. On entering the body (inhalation) it is said to be ten fingers long, on leaving (exhalation) it is twelve.
222. At the time of walking it is twenty-four fingers; running, forty-two; copulating, sixty-five; sleeping, one hundred.
223. O Devi, prana is naturally twelve fingers in length, but while eating or vomiting it is eighteen.
224. If a yogi succeeds in reducing the length of prana by one finger (out of twelve fingers), he obtains desirelessness, with a reduction of two fingers he gets bliss, if reduced by three fingers he gets the energy of love (sex).
225. Reduction of the length of prana by four fingers gives the power of speech (whatever one says comes true); five, telepathy; six, the ability to levitate; seven enables one to move with enormous speed.
226. Reduction of the length of prana by eight fingers gives attainment of the eight siddhis (perfections); nine, attainment of the nine nidhis (riches); ten, ability to change the body into ten forms; eleven, the ability to make the body shadowless.
227. Reduction of the length of prana by twelve fingers enables one to attain the state of hamsa and drink the nectar of the Ganga (to become immortal). The yogi who achieves control over the prana, right from his toes to his head, needs no food and has no desire to eat.

HOW TO REDUCE THE LENGTH OF PRANA? Searching for an answer.

Source: Shiva Swarodaya (Translated in Swara Yoga; Swami Muktibodhananda)