Light a fire and then vocalize the mantra INRI. This mantra is vocalized in two separate syllables: IN-RI, but lengthening the sound of each letter. Now concentrate on the fire that you have lit –candle, oil lamp or burning coals–. Meditate deeply on the fire. Fall asleep meditating on the fire. Invoke the friend who writes this lecture and you will be helped in this practice.
Vocalize the S as a very fine whistle, like the hissing of the rattlesnake.
Samael Aun Weor
Esoteric Course of Kabbalah, chapter 4