Garudapurana 1.235.28

1.235.28

prāṇāyāmairdvādaśabhiryāvatkālaḥkṛto bhavet /
yastāvatkālaparyantaṃ mano brahmaṇi dhārayet //
tasyaiva brahmaṇā proktaṃ dhyānaṃ dvādaśa dhāraṇāḥ /
tuṣyeta niyato yuktaḥ samādhiḥ so 'bhīdhīyate //

The measure of time that is made by twelve breath controls—
he who holds the mind on Brahman for that long a period of time,
for him twelve concentrations are declared by Brahmā to be meditation;
restrained and disciplined, he is content: that is called samādhi.