The Hatha Yoga Pradipika, the oldest known hatha yoga text does not mention “Sun Salutations” but mentions a sūrya-bhedana (sun-piercing) kumbhaka (II, 44 and 48-50) while the Gheraṇḍa Saṁhitā mentions sūrya-bheda kumbhaka (58-59). The oldest documented book with clear depictions of asanas is the Sritattvanidhi, though there is no mention of “Sun Salutations” in the text, it does describe the asanas “Sarpasana” (Bhujangasana), “Gajasana” (Adhomukh Swannasan), “Uttanasana” and series of asanas done in tandem, similar to Sūrya Namaskāra.
The translator of the ancient Sritattvanidhi, Krishnaraja Wodeyar III, was also responsible for arranging for Sri. T. Krishnamacharya to teach yoga at Yogaśālā in Mysore sometime around 1930. Sri. T. Krishnamacharya’s teachings are largely responsible for the modern version of Sūrya Namaskāra as seen in modern day Ashtanga Vinyasa Yoga and the Visesha Vinyasa Sun Salutation subroutine from Vinyasa Krama Yoga, as well as a host of other popular forms of yoga. K. Pattabhi Jois claims to have taught exactly as he had learned from Krishnamacharya, though other than personal testimony, there seems to be no other evidence as to the precise content of Krishnamacharya’s teachings. While Krishnamacharya’s specific sources for his yoga teachings are unclear, it is said that he learned from Sri Ramamohana Brahmachari in the Himilayan Mountains (perhaps Muktinath where his son has visited, but certainly somewhere near the Gandaki River in Nepal) beginning in 1916; however, the source of his teaching (at the Mysore Yogashala or otherwise) is not otherwise documented. Krishnamacharya’s son attests to his father having developed some of his teachings himself. There is the possibility that he may have been influenced by the Mysore Palace Gymnastics Tradition.
Another indication as to the origins of Sūrya Namaskāra is the 1928 Indian publication of “The Ten Point Way of Health” by Raja Bhavan Rao Srinivas (“Bala Sahib”), Pant Pratinidhi of Aundh (1868–1951; Raja of Aundh 1909-1947), followed by later publication in England in 1938. The Raja claims to have practiced the series as a child. And some sources report that only after extensive practice and analysis (and potentially modification) himself did he finally publish the book. Thus, the true origin of the series remains unclear, though it has to be noted that Raja of Aundh, himself never claimed to have invented Surya Namaskar. Further he actually stressed on the ancient origins of this procedure. He helped in popularizing surya namaskar as a simple physical exercise for all round development of an individual in India. He introduced it in schools as a form of education and encouraged even the ordinary man to be physically fit by performing surya namaskar every day. Still, how exactly Sūrya Namaskāra came to be included in the yogic practices of Hatha and Ashtanga Yoga remains unclear.
Other sources which cite early use of “Sun Salutations” are A Short History of Aryan Medical Science from 1896, which claims that in India “there are various kinds of physical exercise indoors and outdoors. But some of the Hindus set aside a portion of their daily worship for making salutations to the Sun by prostrations. This method of adoration affords them so much muscular activity that it takes to some extent the place of physical exercise”.
Early English publications record some ancient methods of sun salutation; however, the do not seem to be related to the modern Sūrya Namaskāra as seen in Yoga practice today. In “A Catalogue raisonnée [sic] of oriental manuscripts”, noted that a short book with 71 leaves with “Tricha calpa vidhi” from “Aditya Puranam” was preserved. He describes the vidhi as “Modes of rendering homage to Sun, with praise and spells; the object being health or delivery from disease”. He further notes the presence of Arghya Pradana, Surya Stotaram, Aditya dvadasa namam – 12 names of the Sun according to the monthly signs of zodiac, Surya Narayana cavacham, Saurashtacshari mantram, and many other elaborate rituals as the part of the vidhi. In Page 148 of the same book he describes a shorter version called “Laghu tricha kalpa vidhi”.
Aditya Hridayam is another ancient practice which involves a variation of Sūrya Namaskāra. It is a procedure of saluting The Sun, taught to Sri Rama by Sage Agastya, before his fight with Ravana. It is described in the “Yuddha Kaanda” Canto 107 of Ramayana.
There are numerous references of praising the Sun for the purpose of good health and prosperity, in Vedas. Some of these Vedic hymns were incorporated into Nitya Vidhi (Daily mandatory routine for a Hindu) for the well being of an individual, through salutations to the Sun. These daily procedures were termed as Surya Namaskara (literally translates as “sun salutations”). Physical prostration to Sun, showing complete surrender of oneself to God, is the main aspect of these procedures. The forms of Surya Namaskar practiced vary from region to region. Two such popular practices are Trucha Kalpa Namaskarah and Aditya Prasna.
Excerpt From Wikipedia Articles, Surya Namaskar and Surya Namaskar Origins