Yoga Rahasya Chapter One verse 34

recapūraka kumbheṣu mano’nusaraṇaṃ smṛtam |
recapūraka kumbhākhyāḥ sarve prāṇavidhārakāḥ ||

Mind should follow the exhale, inhale and retention.
Exhale, inhale and retention all support the vital force.

pūraka - inhalerecaka - exhalekumbhaka - retentionmanas - mindsmṛti - remembrance; memory; mindfulness; the whole body of sacred tradition or what is remembered by human teachers and constantly revisedprāṇa - breath, inward air, vital force

Commentaries and Reflections

TKV Desikachar:

Mind should follow the breath.
ExhaleInhale and Retention support life.
So during Āsana it is desirable that the mind must follow them.”