CHĀNDOGYA UPANISHAD · 4.15.1

य एषो ऽक्षिणि पुरुषो दृश्यत एष आत्मेति होवाच ।
एतद् अमृतम् अभयम् एतद् ब्रह्मेति ।
तद् यद्य् अप्य् अस्मिन् सर्पिर् वोदकं वा सिञ्चति वर्त्मनी एव गच्छति ॥

ya eṣo ’kṣiṇi puruṣo dṛśyata eṣa ātmeti hovāca ।
etad amṛtam abhayam etad brahmeti ।
tad yady apy asmin sarpir vodakaṃ vā siñcati vartmanī eva gacchati ॥

He said: 'The person that is seen in the eye, that is the Self. This is the immortal, the fearless, this is Brahman. Even though they drop melted butter or water on him, it runs away on both sides.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)