Bhagavad Gita 6.26

यतो यतो निश्चरति मनश्चलमस्थिरम् |
ततस्ततो नियमैतदात्मन्येव वशं नयेत्

Translation

Whenever and wherever the restless and unsteady mind wanders, one should bring it back and continually focus it on God.