Patanjali Yoga Sutra 1.5

Sanskrit Sutra

वृत्तयः पंचतय्यः क्लिष्टा अक्लिष्टाः॥५॥

Swami Vivekananda's translation

There are five classes of modifications, (some) painful and (others) not painful.

Chapter link: Yoga Sutra Chapter 1