Bhagavad Gita 6.19

यथा दीपो निवातस्थो नेङ्गते सोपमा स्मृता।योगिनो यतचित्तस्य युञ्जतो योगमात्मनः ॥६.१९॥

yathā dīpo nivātastho neṅgate sopamā smṛtāyogino yatacittasya yuñjato yogamātmanaḥ

As a lamp placed in a windless spot does not flicker, so is the Yogi of a controlled mind, who practices Yoga in the Self, compared.

गीता