Patanjali Yoga Sutra
The 8 Limbs of Ashtanga Yoga (Yama, Niyama, Asana, Pranayama, Pratyahara, Dharana, Dhyana, and Samadhi) can be traced to their philosophical roots in the Yoga Sutra of Patanjali. In the Yoga Sutra each limb is precisely outlined and described as a method for cutting through avidya, ignorance, and developing vivikah khyateh, discerning vision, that enables one to perceive the true nature of the mind/soul, the ultimate reality of being.
This text is said to have been composed by the Indian sage and scholar Patanjali, sometime between the 5th Century BCE and the 4th Century CE. It is a written compilation of yogic knowledge that was already current in the oral tradition. Reportedly, the text nearly disappeared by the 16th Century until it reappeared with Swami Vivekananda in the 19th Century.
I like to listen and repeat along to the Yoga Sutra Chanting Tutorial by Srivatsa Ramaswami (see videos below of each of the 4 chapters).
There are many translations available. For starters, an accessible version is the translation by Sri Swami Satchidananda. For a little more detailed analysis, my favorite online resource so far is at www.swamiji.com. Also, here is a free download of the entire text translated from Sanskrit by Chip Hartranft, who gives it a Buddhist perspective.
Now, who is Patanjali?
Patanjali is said to be swayambhu, a self-born incarnation of Adi Shesha, the infinite serpent upon whom Lord Vishnu rests. I have heard and read that the word Patanjali can be understood as a combination of two Sanskrit words pata ~ fallen or falling & anjali ~ palms folded in prayer.
samadhi pada ~ chapter 1
sadhana pada ~ chapter 2
vibhuti pada ~ chapter 3
kavailya pada ~ chapter 4