Bhagavad Gita 6.19

यथा दीपो निवतस्थो नेङ्गते सोपमा स्मृता |
योगिनो यत्चित्तस्य युञ्जतो योगमात्मन:

Translation

Just as a lamp in a windless place does not flicker, so the disciplined mind of a yogi remains steady in meditation on the Supreme.