Patañjali 
The Yoga Sutras of Patanjali: The Book of the Spiritual Man [EPUB ebook] 

A translation of Yoga Sutras of Patanjali, with word-for-word meanings and precise commentary. New insight into the advanced practices of meditation, kriya yoga and raja yoga. Until Patanjali wrote his original yoga sutras about 4000 years ago, there was no written record about yoga, even though it was already being practiced for centuries. Sutra in Sanksrit means a thread that holds things together. Each of Patanjali's short, sharp and succinct sutras is like a little knot in the thread, to be teased apart for its wisdom.