Patanjali wrote in his book the Raya Yoga Sutras about Yoga – and yoga is the practice of calming the mind. It is the fundamental guide to achieve the highest state, Samadhi, where the personal self is uniting with the universal soul. Where there is no more external influence (karma) affecting the mind and you dive into bliss, self-realization, and wisdom.
Most of the gurus of the yogic tradition wrote about the sutras, and made science about them.
https://free-ebooks-for-download-b5504.firebaseapp.com/po4dMlz1/drEBO2mk.html
Download a book about Raja Yoga from Swami Sivananda for free
https://www.dlshq.org/download/download.htm
Recommended are the books: Bhagavad Gita, Thought Power, Essence of Yoga, Kundalini Yoga