kaṭhopaniṣad - adhyāya 2, vallī 1

The Self-Existent Lord pierced the openings of the senses outward; therefore, one looks outward and not within oneself. Some rare, wise seeker, desiring immortality, closes their eyes and beholds the indwelling Self.

The immature follow outward desires and fall into the wide-spread snare of death. But the wise, knowing the nature of immortality, do not seek the permanent among things that are transitory.

By which one perceives form, taste, smell, sounds, and tactile contacts—by that same Self one also knows. What remains here unknown? This, verily, is That.

The wise man, having realized that the great, all-pervading Self by which one perceives all things in both the dream state and the waking state, ceases to grieve.

He who knows this Self, the enjoyer of honey, the living soul, ever near, the Lord of what has been and what will be, does not shrink away from It. This, verily, is That.

He who perceives Him who was born of austerity, who was born before the waters, who stands hidden in the secret place of the heart and has manifested Himself along with the elements—this, verily, is That.

She who is the embodiment of all deities, who manifests through the vital breath, who dwells hidden in the heart, and who was born along with the elements—this, verily, is That.

Agni, the All-Knower, hidden in the two friction-sticks like a child well-guarded in the womb by a mother, is adored day after day by wakeful men who offer oblations. This, verily, is That.

That from which the sun rises and into which it sets—in That all the gods are established, and none can ever transcend It. This, verily, is That.

Whatever is here, that is there; whatever is there, that is here. He who sees any difference here goes from death to death.

This truth is to be attained by the mind alone; there is no diversity here at all. He who sees diversity in this world goes from death to death.

The Purusha, no larger than a thumb, dwells in the center of the being. He is the Lord of the past and the future, and after knowing Him, one no longer fears. This, verily, is That.

The Purusha, no larger than a thumb, is like a flame without smoke. He is the Lord of the past and the future; He is the same today and He shall be the same tomorrow. This, verily, is That.

As rainwater falling on a high mountain peak runs down in various directions among the hills, so too, the man who perceives the qualities of the Self as distinct and separate runs after them, lost in the cycle of change.

As pure water poured into pure water becomes the same, so too, O Gautama, does the self of the sage who has known the Truth become one with the Divine.