Śrīmad-Bhāgavatam · Text 3.28.10
Who is speaking and story frame
मनोऽचिरात्स्याद्विरजं जितश्वासस्य योगिन: ।
वाय्वग्निभ्यां यथा लोहं ध्मातं त्यजति वै मलम् ॥ १० ॥
mano ’cirāt syād virajaṁ
jita-śvāsasya yoginaḥ
vāyv-agnibhyāṁ yathā lohaṁ
dhmātaṁ tyajati vai malam
The yogīs who practice such breathing exercises are very soon freed from all mental disturbances, just as gold, when put into fire and fanned with air, becomes free from all impurities.
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