Study a single sutra by selecting the pada (chapter) and then the sutra (verse).
Source: English translation from The Yoga Sutras of Patanjali (Sri Swami Satchidananda)
The modifications of the life-breath are either external, internal or stationary. They are to be regulated by space, time and number and are either long or short.
Source: English translation from Light on the Yoga Sutras of Patanjali (B.K.S. Iyengar)
Pranayama has three movements: prolonged and fine inhalation, exhalation and retention; all regulated with precision according to duration and place.
Source: How to Know God: The Yoga Aphorisms of Patanjali (Swami Prabhavananda, Christopher Isherwood)
The breath may be stopped externally, or internally, or checked in mid-motion, and regulated according to place, time and a fixed number of moments, so that the stoppage is either protracted or brief.
Source: English translation from The Heart of Yoga (T.K.V. Desikachar)
It involves the regulation of the exhalation, the inhalation, and the suspension of the breath. The regulation of these three processes is achieved by modulating their length and maintaining this modulation for a period of time, as well as directing the mind into the process. These components of breathing must be both long and uniform.
Source: English translation of the Yoga Sutras of Patanjali (Swami Jnaneshvara Bharati)
That pranayama has three aspects of external or outward flow (exhalation), internal or inward flow (inhalation), and the third, which is the absence of both during the transition between them, and is known as fixedness, retention, or suspension. These are regulated by place, time, and number, with breath becoming slow and subtle.