Sutra 2.32: sauca-santosa-tapah-svâdhyâyesvara-prañidhânâni niyamâh
Translation: Cleanliness and purity of body and mind, an attitude of contentment, discipline, self-study and reflection on sacred words, and an attitude of surrender are the observances or practices of self-training, and are the second rung on the ladder of yoga, otherwise known as the Niyamas.