Bhagavad Gita · 10.15

स्वयमेवात्मनात्मानं वेत्थ त्वं पुरुषोत्तम।भूतभावन भूतेश देवदेव जगत्पते॥

svayam evātmanātmānaṁ vettha tvaṁ puruṣhottama bhūta-bhāvana bhūteśha deva-deva jagat-pate

Indeed, you alone know yourself by yourself, O Supreme Person, creator of all beings, lord of all beings, God of gods, lord of the universe.

— Bhagavad Gita 10.15

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)