KAṬHA UPANISHAD · 2.1.13

अङ्गुष्ठमात्रः पुरुषो ज्योतिरिवाधूमकः ।
ईशानो भूतभव्यस्य स एवाद्य स उ श्वः । एतद्वै तत् ॥ १३॥

aṅguṣṭhamātraḥ puruṣo jyotirivādhūmakaḥ ।
īśāno bhūtabhavyasya sa evādya sa u śvaḥ । etadvai tat ॥ 13॥

The Purusha that is within is no larger than the finger of a man; He is like a blazing fire that is without smoke, He is lord of His past and His future. He alone is today and He alone shall be tomorrow. This is the thing thou seekest.