Bg 6.19

yatha dipo nivata-stho
nengate sopama smrta
yogino yata-cittasya
yuñjato yogam atmanah

Word for word: 
yatha — as; dipah — a lamp; nivata-sthah — in a place without wind; na — does not; ingate — waver; sa — this; upama — comparison; smrta — is considered; yoginah — of the yogi; yata-cittasya — whose mind is controlled; yuñjatah — constantly engaged; yogam — in meditation; atmanah — on transcendence.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As a lamp in a windless place does not waver, so the transcendentalist, whose mind is controlled, remains always steady in his meditation on the transcendent Self.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
A truly Krishna conscious person, always absorbed in transcendence, in constant undisturbed meditation on his worshipable Lord, is as steady as a lamp in a windless place.