BṚHADĀRAṆYAKA UPANISHAD · 2.4.9

स यथा वीणायै वाद्यमानायै न बाह्याञ् छब्दाञ् छक्नुयाद् ग्रहणाय वीणायै तु ग्रहणेन वीणावादस्य वा शब्दो गृहीतः ॥

sa yathā vīṇāyai vādyamānāyai na bāhyāñ chabdāñ chaknuyād grahaṇāya vīṇāyai tu grahaṇena vīṇāvādasya vā śabdo gṛhītaḥ ॥

'And as the sounds of a lute, when played, cannot be seized externally (by themselves), but the sound is seized, when the lute is seized or the player of the lute;