Chapter 10 · The Divine Glories · Arjuna said
Bhagavad Gita 10.15 — Only He knows Himself
स्वयमेवात्मनात्मानं वेत्थ त्वं पुरुषोत्तम। भूतभावन भूतेश देवदेव जगत्पते ॥
svayamevātmanātmānaṃ vettha tvaṃ puruṣottama | bhūtabhāvana bhūteśa devadeva jagatpate ||
Meaning
O Supreme Person, creator and Lord of all beings, God of gods and master of the world — you alone know yourself, through yourself.