Soham (Sanskrit) (English Wikipedia)

Chawdhri, L. R. (2007). Secrets of Yantra, Mantra and Tantra. Sterling Publishers Pvt. Ltd. p. 93. ISBN 978-1-84557-022-4. "Ha" is the outgoing breath and "sa" is the ingoing breath.
Nair, Sreenath (2007). Restoration of Breath: Consciousness and Performance. Rodopi. p. 100 ff. ISBN 978-90-420-2306-2.
Margaret Stutley; Anonymous (1977). A Dictionary of Hinduism. London: Routledge. p. 372. ISBN 978-0-429-62754-5. OL 35543927M. Wikidata Q110087969. The Hamsa symbolizes knowledge and the life-force or cosmic breath (prana), 'ham' being its exhalation, and 'sa', its inhalation which is regarded as the return of the individual life-force to brahman, its cosmic source. {{cite book}}: |author2= has generic name (help)

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Olivelle 1992, pp. 80–81, 210 with footnotes. Olivelle, Patrick (1992). The Samnyasa Upanisads. Oxford University Press. ISBN 978-0195070453.
Olivelle 1992, pp. 80–81. Olivelle, Patrick (1992). The Samnyasa Upanisads. Oxford University Press. ISBN 978-0195070453.
Olivelle 1992, pp. 210, 216. Olivelle, Patrick (1992). The Samnyasa Upanisads. Oxford University Press. ISBN 978-0195070453.
Olivelle 1992, pp. 227, 229. Olivelle, Patrick (1992). The Samnyasa Upanisads. Oxford University Press. ISBN 978-0195070453.
Olivelle 1992, pp. 156. Olivelle, Patrick (1992). The Samnyasa Upanisads. Oxford University Press. ISBN 978-0195070453.
Olivelle 1992, pp. 160–161, 165–166. Olivelle, Patrick (1992). The Samnyasa Upanisads. Oxford University Press. ISBN 978-0195070453.

"Yoga Sikha Upanishad". Retrieved 2009-05-17. 6.53 The prana goes out with sound "ham" and goes in with the word "sa", and all beings naturally chant the mantra "Hamsa, Hamsa" (while exhaling and inhaling).
"Bhaja Gaureesam". Retrieved 2009-05-17.
"Gowresa Ashtakam". Retrieved 2009-05-17.
"Shakthi Mahimnah Stotram". Retrieved 2009-05-17.
"Tripurasundari Vijaya Sthava". Retrieved 2009-05-17.
"Adi Shankara's Vakya Vritti". Retrieved 2009-05-17.

"Shiva Svarodaya (51)". Retrieved 2009-05-17. The Shiva Svarodaya scripture's verse 51 says, "The process of exhalation is said to contain the letter ham, and the inhalation contains the letter sa."
"Gheranda Samhita 5:84". Retrieved 2009-05-17. Gheranda Samhita 5:84 indicates, "Breath of every person, in entering, makes the sound of 'sa', and in coming out (bahiryati), that of 'ham.' "

"Vijnana Bhairava". Archived from the original on 2006-08-21. Retrieved 2009-05-17.

"Letter from Swami Muktananda to Franklin Jones, April 23, 1968". Retrieved 2009-05-17. Harmonize the repetition of mantra with the breathing as follows: With "So" take it in and with "ham" bring it out. (...) When one's mind is fixed on "So" with the incoming breath and on "ham" with the outgoing breath it is mantra-japa. (...) Your beauty, your energy, your duty, your religion, your Guru and guide; your study, worship and prayer -- all lie in engaging yourself to the remembrance and repetition of "So'ham", "So'ham". This is my instruction, this is my precept. This is to be followed or practiced, and reflected upon devoutly.

Margaret Stutley; Anonymous (1977). A Dictionary of Hinduism. London: Routledge. p. 372. ISBN 978-0-429-62754-5. OL 35543927M. Wikidata Q110087969. The Hamsa symbolizes knowledge and the life-force or cosmic breath (prana), 'ham' being its exhalation, and 'sa', its inhalation which is regarded as the return of the individual life-force to brahman, its cosmic source. {{cite book}}: |author2= has generic name (help)

The Upanishads, Part 1 1879, p. 313. Müller gives the footnote: "Asau purushah should probably be omitted", taking these words as an explanatory gloss that was accidentally incorporated in the text.

"Gandharva Tantra (abstract)". Retrieved 2009-05-17.
"Kularnava Tantra". Retrieved 2009-05-17. Ham-Sah is the pathway breath takes in living creatures. This mantra exists in the form of exhalation and inhalation

"Vijnana Bhairava". Archived from the original on 2006-08-21. Retrieved 2009-05-17.
"Muktabodha on-line library Kashmir Series of Texts and Studies". Archived from the original on February 4, 2009. Retrieved 2009-05-17.

Margaret Stutley; Anonymous (1977). A Dictionary of Hinduism. London: Routledge. p. 372. ISBN 978-0-429-62754-5. OL 35543927M. Wikidata Q110087969. The Hamsa symbolizes knowledge and the life-force or cosmic breath (prana), 'ham' being its exhalation, and 'sa', its inhalation which is regarded as the return of the individual life-force to brahman, its cosmic source. {{cite book}}: |author2= has generic name (help)