Katha Upanishad Verse 2.1.14
Yama warns against the perception of duality. Just as rain water falling on a mountain peak scatters and runs down on all sides, those who perceive differences between manifested forms remain distracted and chase after external appearances.
Sanskrit Verse
यथोदकं दुर्गे वृष्टं पर्वतेषु विधावति ।
एवं धर्मान् पृथक् पश्यंस्तानेवानुविधावति ॥ १४ ॥
Transliteration
yathodakaṃ durge vṛṣṭaṃ parvateṣu vidhāvati |
evaṃ dharmān pṛthak paśyaṃstānevānuvidhāvati || 14 ||
Translation
As rain water, (falling) on the mountain top, runs down over the rocks on all sides; similarly, he who sees difference (between visible forms) runs after them in various directions.

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