Śrīmad-Bhāgavatam · Text 12.3.47
Who is speaking and story frame
यथा हेम्नि स्थितो वह्निर्दुर्वर्णं हन्ति धातुजम् ।
एवमात्मगतो विष्णुर्योगिनामशुभाशयम् ॥ ४७ ॥
yathā hemni sthito vahnir
durvarṇaṁ hanti dhātu-jam
evam ātma-gato viṣṇur
yoginām aśubhāśayam
Just as fire applied to gold removes any discoloration caused by traces of other metals, Lord Viṣṇu within the heart purifies the minds of the yogīs.
Read the purport on Vedabase.ioFrom Canto 10, chapter 14 onward, the translation and purports were completed by Śrīla Prabhupāda's disciples after his departure, and published by the Bhaktivedanta Book Trust.