Rishi Patañjali describes yoga as a method with eight different limbs- ie Ashtanga Yoga – in sūtra 2.29:
yama niyama āsana prāṇāyāma pratyāhāra dhāraṇā dhyāna samādhayō `ṣṭāv aṅgāni
This sutra names the eight limbs of yoga (ashtanga yoga). Following the instructions will bring the seeker to his destination (yoga state). The eight stages are built on top of each other, with finer and finer levels being fathomed from level to level, but the levels are not practiced in isolation but are interlinked. The eight limbs are (by clicking on the limb you will get to the corresponding article):