Traditional Yoga, as set out by patanjali in his Yoga sutras, consists of eight ‘paths’. The first five are called bahiranga sadhana (external aids to Yoga), and the last three are called antaranga sadhana (internal aids to Yoga).
Pratyahara is the first of the antaranga sadhana (internal aids to Yoga) and the fifth path of Yoga. Pratyahara means withdrawal of senses from the external and focussing it internally. This can happen spontaneously for example, when the body and mind are quiet and settled in the moments before sleep.
There are Yoga asanas that naturally induce pratyahara. Child pose draws the body in on itself, the eyes are cast down, the ears are covered by the arms and the nose is close to the earth – the senses withdraw as the mind can’t help but become attuned to the pattern of breathing.
Pranayama also naturally induces pratyahara – especially when practices for several minutes with the eyes closed, in a quiet place.