Yoga Rahasya Chapter One verse 34

reca-pūraka-kumbheṣu mano’nusaraṇaṃ smṛtam |
reca-pūraka-kumbhākhyāḥ sarve prāṇavidhārakāḥ ||

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

recaka - exhalepūraka - inhalekumbhaka - retentionmanas - mindanu - followsmṛti - remembrance; memory; mindfulness; the whole body of sacred tradition or what is remembered by human teachers and constantly revisedsarva - allprāṇa - vital force; the breath of life; breath; inward air

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.”