Study a single sutra by selecting the pada (chapter) and then the sutra (verse).
Source: How to Know God: The Yoga Aphorisms of Patanjali (Swami Prabhavananda, Christopher Isherwood)
When a man becomes steadfast in his abstention from greed, he gains knowledge of his past, present and future existences.
Source: English translation of the Yoga Sutras of Patanjali (Swami Jnaneshvara Bharati)
When one is steadfast in non-possessiveness or non-grasping with the senses (aparigraha), there arises knowledge of the why and wherefore of past and future incarnations.