Possibly the oldest extant text about Hatha Yoga, The Hatha Yoga Pradipika was written about the 15th century CE, by Swami Swatmarama, a disciple of Swami Goraknath. - Sacred Texts.
Possibly the oldest extant text about Hatha Yoga, The Hatha Yoga Pradipika was written about the 15th century CE, by Swami Swatmarama, a disciple of Swami Goraknath