Kshurika Upanishad: Kshurika means knife. Kshurikopanishad teaches us how to cut our attachments using the knife of wisdom to attain liberation. It tells us how to practice meditation by concentrating the mind on various parts of the body and release the energy hidden in various centers starting with the one at the base of the spine and moving gradually upward to the neck region where the three main nerves, Ida, Pingala and Sushumna are said to be located. The Upanishad also prescribes breathing techniques, detachment and meditation on Om and renunciation for attaining immortality.
Tejo Bindu Upanishad contains a dialogue between Lord Muruga (Karthikeya) and Lord Shiva on philosophical topics like Jeevanmukti, realization of Atman, nature of Chinmatra etc. PARAM-DHYANA (the supreme meditation) should be upon Tejo-bindu (the seed or source of spiritual light), which is the Atma of the universe, which is seated in the heart, which is of the size of an atom, which pertains to Shiva, which is quiescent and which is gross and subtle, as also above these qualities. That alone should be the Dhyana of the Munis as well as of men, which is full of pains, which is difficult to meditate on, which is difficult to perceive, which is the emancipated one, which is decayless and which is difficult to attain.
Yama (forbearance), Niyama (religious observance), Tyaga (renunciation), Mouna (silence) according to time and place, Asana (posture), Mulabandha, seeing all bodies as equal, the position of the eye; Prana-samyamana (control of breath), Pratyahara (subjugation of the senses), Dharana, Atma-Dhyana and Samadhi - these are spoken of as the parts (of Yoga) in order. That is called Yama in which one controls all his organs (of sense and actions) through the Vijnana that all is Brahman; this should be practised often and often.
Niyama, in which there is the supreme bliss enjoyed through the flowing (or inclination) of the mind towards things of the same (spiritual) kind, (viz., Brahman) and the abandoning of things differing from one another is practised by the sages as a rule. In Tyaga (renunciation), one abandons the manifestation (or objects) of the universe through the cognition of Atman that is Sat and Chit. This is practised by the great and is the giver of immediate salvation.
Mouna (the silence), in which, without reaching That, speech returns along with mind, is fit to be attained by the Yogins and should be ever worshipped by the ignorant (even). That should be known as Asana (posture), in which one has with ease and without fatigue (uninterrupted) meditation of Brahman; that is described by the word Kala (time), that is endless bliss and that is secondless. Everything else is the destroyer of happiness.
Dhyana Bindu Upanishad: Even if sin should accumulate to a mountain extending over many Yojanas (distance), it is destroyed by Dhyana-Yoga. At no time has been found a destroyer of sins like this. Bijakshara (seed-letter) is the supreme Bindu. Nada (spiritual sound) is above it. When that Nada ceases along with letter, then the Nada-less is supreme state. The Yogin who considers as the highest that which is above Nada, which is Anahata, has all his doubts destroyed.
If the point of a hair be divided into one hundred thousand parts, this (Nada) is one-half of that still further divided; and when (even) this is absorbed, the Yogin attains to the stainless Brahman. One who is of a firm mind and without the delusion (of sensual pleasures) and ever resting in Brahman, should see like the string (in a rosary of beads) all creatures (as existing) in Atman like odour in flowers, ghee in milk, oil in gingelly seeds and gold in quartz.
The one Akshara (letter OM) should be contemplated upon as Brahman by all who aspire for emancipation. Prithvi, Agni, Rig-Veda, Bhuh and Brahma -- all these (are absorbed) when Akara (A), the first Amsa (part) of Pranava (OM) becomes absorbed. Antariksha, Yajur-Veda, Vayu, Bhuvah and Vishnu, the Janardana - all these (are absorbed) when Ukara (U), the second Amsa of Pranava becomes absorbed. Dyur, sun, Sama-Veda, Suvah and Maheshvara - all these (are absorbed) when Makara (M), the third Amsa of Pranava becomes absorbed.
Akara is of (Pita) yellow colour and is said to be of Rajo-Guna; Ukara is of white colour and of Sattva-Guna; Makara is of dark colour and of Tamo-Guna.
He who does not know Omkara as having eight Angas (parts), four Padas (feet), three Sthanas (seats) and five Devatas (presiding deities) is not a Brahmana.
Pranava is the bow. Atman is the arrow and Brahman is said to be the aim. One should aim at it with great care and then he, like the arrow, becomes one with It. When that Highest is cognised, all Karmas return (from him, viz., do not affect him). The Vedas have Omkara as their cause. The Swaras (sounds) have Omkara as their cause.
The three worlds with (all) the locomotive and the fixed (ones in them) have Omkara as their cause.
Brahmavidya Upanishad teaches methods of attaining Brahman through meditation. It emphasizes the role of Guru. It also proclaims that Sruthi is more important than pramana. The syllable OM is the Brahman. The syllable OM is the Brahman. Thus, verily, teach the Brahman-knowers; Body, location, time and dying away of this syllable.
I - The body of the sound OM:
There are three gods and three worlds, three Vedas and three fires. Three moras and the half mora in that trisyllabic, blissful one. The Rig Veda, Grahapatya proclaim the earth and Brahman as God. It is the body of the "a" sound, as expounded by the Brahman-knowers.
The Yajur Veda and the mid-region, and the fire Dakshina, and the holy god Vishnu, this is the "u" sound proclaimed to us. The Sama Veda and heaven, the Ahavaniya fire also, and Ishvara, the highest (or supreme) god. Thus is the "m" sound proclaimed to us.
II - The location of the sound OM:
In the midst of the brain-conch, like the sun-shine glitters the "a". Within it is situated, the "u" sound of moon-like splendor. The "m" sound too, like the fire, smokeless, resembling a lightning flash. Thus shine the three moras, like the Moon, the Sun and the fire. There upon a pointed flame, like a torch light exists. Know it as the half mora, which one writes above the syllable.
III - The terminus of the sound OM:
Yet one, like a pointed flame subtle, like lotus-fiber, shines the Sun-like cerebral artery - (passing through it) penetrates (the OM). Through the Sun and seventy two thousand arteries, breaks through the head and remains as bringer of blessings to all - pervading the whole Universe.
IV - The vanishing, fading away of the sound OM:
And just as the sound of a metal utensil - or of a gong dies in silence - so he, who seeks the All lets the OM sound fade away in silence. For that wherein the sound fades away is the Brahman, the higher. The whole sound is Brahman and conduces to immortality.