One verse

Srimad Bhagavatam 12.6.39

12.6.39

ततोऽभूत्‍त्रिवृदोंकारो योऽव्यक्तप्रभव: स्वराट् । यत्तल्ल‍िङ्गं भगवतो ब्रह्मण: परमात्मन: ॥ ३९ ॥

tato ’bhūt tri-vṛd oṁkāro yo ’vyakta-prabhavaḥ sva-rāṭ yat tal liṅgaṁ bhagavato brahmaṇaḥ paramātmanaḥ

tataḥ
from that
abhūt
came into being
tri-vṛt
threefold
oṁkāraḥ
the syllable om
yaḥ
which
avyakta
not apparent
prabhavaḥ
its influence
sva-rāṭ
self-manifesting
yat
which
tat
that
liṅgam
the representation
bhagavataḥ
of the Supreme Personality of Godhead
brahmaṇaḥ
of the Absolute Truth in His impersonal aspect
parama-ātmanaḥ
and of the Supersoul

From that transcendental subtle vibration arose the oṁkāra composed of three sounds. The oṁkāra has unseen potencies and manifests automatically within a purified heart. It is the representation of the Absolute Truth in all three of His phases — the Supreme Personality, the Supreme Soul and the supreme impersonal truth.