The Yogasūtra of Patañjali is an iconic text in the history of yoga. Sometimes referred to as the Pātañjalayogaśāstra this 4th to 5th century CE text is a systematic explanation of the metaphysical school of sāṃkhya from a practical perspective. It contains key teachings on the eight limbs of yoga (including morality, posture and breathing), stages of meditation, and superhuman capabilities. If you have a practice of yoga or meditation your practice is informed by this text.