SB 7.15.34
evam abhyasyatas cittam
kalenalpiyasa yateh
anisam tasya nirvanam
yaty anindhana-vahnivat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When the yogi regularly practices in this way, in a short time his heart becomes fixed and free from disturbance, like a fire without flames or smoke.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Nirvana means the cessation of all material desires. Sometimes desirelessness is understood to imply an end to the workings of the mind, but this is not possible. The living entity has senses, and if the senses stopped working, the living entity would no longer be a living entity; he would be exactly like stone or wood. This is not possible. Because he is living, he is nitya and cetana — eternally sentient. For those who are not very advanced, the practice of yoga is recommended in order to stop the mind from being agitated by material desires, but if one fixes his mind on the lotus feet of Krsna, his mind naturally becomes peaceful very soon. This peace is described in Bhagavad-gita (5.29):
bhoktaram yajña-tapasam
sarva-loka-mahesvaram
suhrdam sarva-bhutanam
jñatva mam santim rcchati
If one can understand Krsna as the supreme enjoyer, the supreme proprietor of everything, and the supreme friend of everyone, one is established in peace and is free from material agitation. However, for one who cannot understand the Supreme Personality of Godhead, the practice of yoga is recommended.