Katha Upanishad Verse 2.2.12

True and eternal bliss belongs only to the wise who perceive the one internal Ruler—the Atman—residing within their own heart. He who makes his one form diverse is the source of all joy.

Sanskrit Verse

एको वशी सर्वभूतान्तरात्मा एकं रूपं बहुधा यः करोति ।
तमात्मस्थं ये’नुपश्यन्ति धीरास्तेषां सुखं शाश्वतं नेतरेषाम् ॥ १२ ॥

Transliteration

eko vaśī sarvebhūtāntarātmā ekaṃ rūpaṃ bahudhā yaḥ karoti |
tamātmasthaṃ ye’nupaśyanti dhīrāsteṣāṃ sukhaṃ śāśvataṃ netareṣām || 12 ||

Translation

Sole, controller, the internal atman of all living things who makes his own form diverse to the intelligent who realizes him as seated in the self, eternal bliss is theirs, not others.