Bhagavad Gita 5.21

बाह्यस्पर्शेष्वसक्तात्मा विन्दत्यात्मनि यत्सुखम् ।
स ब्रह्मयोगयुक्तात्मा सुखमक्षयमश्नुते  ॥

bāhya-sparśeṣv-asaktātmā vindaty-ātmani yat-sukham
sa brahma-yoga-yuktātmā sukham-akṣayam-aśnute – 5.21

Whatever happiness one derives inwardly from the Self, by not clinging to and associating with the objects around, the same happiness in interminable measure he gets on identifying with Brahman (and gaining the resulting expanse).